Here's what the US Transportation Security Administration (TSA) have to say and they are probably the toughest. Each country has different security requirements, but much of the information will be similar for air travel throughout the world.
Baggage Items Prohibited or Restricted in Airports and Airplanes
For some passengers, going to the airport can be stressful, especially worrying about whether everything in their bags are allowed in the airport or on the airplane, and this extra stress may even contribute to their fear of flying. However, if you take some time to get familiar with common security rules, the basic baggage rules followed by many airlines, and especially how to be smart about what to put in your carry-on baggage, going through airport security will be a lot easier.
Because of the constantly changing security threats to aviation, most countries have many restrictions on what you can carry on an airplane, and other security restrictions that affect your air travel experience. However, if you take some time to get familiar with the basic security rules, you'll probably avoid any problems when you go to the airport.
Items That Are Completely Banned
The following items are completely banned from aircraft, and should not be brought to the airport:
Explosive and Incendiary Materials: Gunpowder (including black powder and percussion caps), dynamite, blasting caps, fireworks, flares, plastic explosives, grenades, replicas of incendiary devices, and replicas of plastic explosives.
Flammable Items: Gasoline, gas torches, lighter fluid, cooking fuel, other types of flammable liquid fuel, flammable paints, paint thinner, turpentine, aerosols (exceptions for personal care items, toiletries, or medically related items).
Gases and Pressure Containers: Aerosols (with the exception of personal care items or toiletries in limited quantities in containers sized three ounces or smaller), carbon dioxide cartridges, oxygen tanks (scuba or medical), mace, tear gas, pepper spray, self-inflating rafts, and deeply refrigerated gases such as liquid nitrogen.
Matches: All matches are banned from checked baggage, and strike-anywhere matches are banned completely from aircraft, but you can have a single book of safety (non-strike anywhere) matches with you in the passenger cabin.
Oxidizers and Organic Peroxides: Bleach, nitric acid, fertilizers, swimming pool or spa chemicals, and fiberglass repair kits.
Poisons: Weed killers, pesticides, insecticides, rodent poisons, arsenic, and cyanides.
Infectious Materials: Medical laboratory specimens, viral organisms, and bacterial cultures.
Corrosives: Drain cleaners, car batteries, wet cell batteries, acids, alkalis, lye, and mercury.
Organics: Fiberglass resins, peroxides.
Radioactive Materials: There are some exceptions for implanted radioactive medical devices. Contact your airline for details on how to ship other radioactive materials.
Magnetic Materials: Strong magnets such as those in some loudspeakers and laboratory equipment.
Other Dangerous Items: Tear gas, spay paint, swimming pool or spa chlorine, and torch lighters.
Note: If you are in any doubt about whether your item may be hazardous, you should bring it to the attention of either your airline or the security screener.
Items Allowed Only in Checked Baggage
The Transportation Security Administration (TSA) has prohibited the following items from airplane cabins and carry-on baggage but may (with some exceptions) be carried as checked baggage:
Sporting Goods: Bats (baseball, softball, cricket), hockey sticks, lacrosse sticks, bows and arrows, ski poles and spear guns golf clubs, and pool cues.
Knives: Knives of any length, composition or description (except for plastic or round bladed butter knives), swords, machetes, and martial arts weapons such as throwing stars.
Cutting Instruments: Carpet knives and box cutters (and spare blades), any device with a folding or retractable blade, ice picks, straight razors, and metal scissors with pointed tips, are only allowed in checked baggage. Small scissors with a cutting edge less than four inches (10 cm) are allowed in the cabin.
Firearms: Pistols, flare guns, BB guns, rifles, and other firearms must be unloaded, packed in a locked hard-sided container, and declared to the airline at check-in. There are limited exceptions to the firearms and ammunition rules for law enforcement officers. In the United States, federal laws apply to aircraft and to the secure areas of the airport such as the gate areas. State or local laws concerning the carrying of concealed or unconcealed weapons do not apply. Attempting to enter the secure area of the terminal with weapons, even accidentally, may lead to your arrest.
Firearm Replicas: Realistic replicas of firearms must be carried as checked baggage. Toy weapons that are not realistic are allowed in checked or carry-on baggage.
Firearm Parts: They should be treated like firearms and only carried in checked baggage.
Ammunition: In the US, small arms ammunitions for personal use must also be declared to the airline at check-in, and must be securely packed in fiber, wood or metal boxes or other packaging specifically designed to carry small amounts of ammunition. Ammunition, if properly packaged, can also be carried in the same hard-sided case as an unloaded firearm. You should check with the airline to see if it has additional restrictions on either firearms or ammunition.
Paintball Guns: Compressed air guns, including paintball guns, may be carried in checked luggage without the compressed air cylinder attached. Compressed gas cylinders are not allowed on aircraft.
Tools: Tools greater than seven inches in length can only be carried as checked baggage. Also, power tools such as drills should also be in checked baggage. Shorter tools, such as wrenches, screwdrivers, and pliers, may be carried in carry-on baggage. Any tool with a sharp or cutting edge like a hand saw, box cutter, or drill bit are also limited to checked baggage. If you have a toolbox in checked baggage, make sure you check every compartment to make sure that your toolbox does not have any containers with flammable liquids, utility lighters, micro torches, or other banned items. Larger equipment like a step ladder or circular saw should be checked.
Dry Ice (frozen carbon dioxide): Up to four pounds (1.8 kg) may be carried on board for packing perishables providing the package is vented.
Hazardous Items Allowed in Carry-on Bags and the Passenger Cabin
There are a number of items that could be considered hazardous or dangerous that are actually allowed in the passenger cabin, including your carry-on baggage:
Small Hand Tools: Most hand tools that are less than seven inches (18 cm) in length and that don't have sharp cutting edges can be taken into the passenger cabin. This would include tools like wrenches, screwdrivers, and pliers.
Matches and Lighters: You can have a single book of safety (non-strike anywhere) matches with you in the passenger cabin, either on your person or in your carry-on baggage. You can have a common lighter with you on your person or in your carry-on baggage. In the US, lighters with fuel are prohibited in checked baggage, unless they adhere to the Department of Transportation (DOT) exemption, which allows up to two fueled lighters if properly enclosed in a DOT approved case.
Things You Should Never Put in Checked Baggage
There are many items that are not hazardous or prohibited that you can carry either in checked baggage, in carry-on baggage, or on your person. However, if it is an item that is hard to replace, very expensive, or necessary for your health and well being, then you should never put it in checked baggage:
Money Related Items: Cash, credit cards, travelers checks, blank checkbooks, securities, and anything else that has monetary value or should either be on your person or in your carry-on baggage. If you lose money-related items in your checked baggage, airlines are not obligated to compensate you.
Jewelry: Necklaces, rings, diamonds, other precious stones, gold, silver, other precious metals, expensive watches, and other small and valuable items like these should also stay out of checked baggage. Like the situation with money, the airline isn't obligated to compensate you for the loss.
Laptops and Electronic Devices: Laptops, cell phones, and other small personal electronic devices should remain on your person or in your carry-on bags.
Medically Related Items: Prescription medication, other medications, and other medical items should remain with you in the cabin.
Other Items: If it is small and valuable, or if replacing it would be difficult or expensive, then keep it with you in the cabin. Examples include passports and other identification, keys; eyeglasses or sunglasses; photos, exposed film, tickets, art, boarding passes, travel vouchers, mail, financial records, business documents, manuscripts, heirlooms, collectible items, favorite toys, portable data storage devices like flash drives, and software. If you have something else that is small and that you don't want to lose, keep it with you.
Last Minute Bag Check
Sometimes on full or nearly full flights, the airplane may run out of room, and you may be forced to check your carry-on bag at the gate. You should pack your carry-on bag in a manner so that if it must be gate-checked, you can quickly remove the fragile, valuable and critical items and have them in a smaller bag that you can fit under a seat.
Restrictions on Liquids, Gels, and Aerosols
On 10 August 2006, authorities in the United Kingdom uncovered an alleged plot to sabotage as many as 10 US airliners traveling from the United Kingdom to the United States, reportedly by using liquid and gel based explosives. Since then, the US and most other countries have restricted what liquids and gels a passenger may have in the passenger cabin: In the US, the general TSA restrictions are as follows:
Passengers may bring into the secure area of the airport liquid and gel products, so long as each individual container has a capacity of no greater than 3.4 fluid ounces (100 ml), and all of these small containers can fit in quart-size, zip-top, clear plastic bag. The TSA suggestion for a zip-top is a loose requirement. If you only have a few small containers, you don't need an additional zip-top bag.
Snow globes and similar liquid-filled decorations, no matter what size, can only be carried in checked luggage.
Passengers may not pass through the security screening with gel or beverage containers of greater capacity unless they fall under one of the exemptions described below.
Note: Once a passenger has passed through security screening, they can purchase any size beverage and other liquid or gel products in the terminal and take them on to the plane.
Exceptions to the Restrictions for Liquids, Gels and Aerosols
All prescription drugs and over-the-counter medications including insulin and other diabetes medical supplies, petroleum jelly, K-Y jelly, eye drops, and saline solution.
Liquids including water, juice, or liquid nutrition or gels for passengers with a disability or medical condition.
Life-support and life-sustaining liquids such as bone marrow, blood products, and transplant organs.
Items used to augment the body for medical or cosmetic reasons such as mastectomy products, prosthetic breasts, bras or shells containing gels, saline solution, or other liquids.
Frozen gels or liquids are permitted if required to cool medical and infant/child exemptions. Ice is permitted as long as there is no melted liquid present.
Baby formula, breast milk, juice or water for a traveling infant small child.
Breast milk is in the same category as liquid medications. A mother flying without her child should be able to bring breast milk through the checkpoint, provided it is declared prior to screening.
If you have liquids, aerosols, or gels the meet these exceptions, they can be in containers larger than 3.4 fluid ounces (100 ml), and do not have to be inside of a quart sized plastic bag, but do have to be declared at the security checkpoint.
Once past the security checkpoint, you are free to buy liquid gel products of any size within the secure areas of the airport terminal and take them on board.
Note: Solid cosmetics and personal hygiene items such as lipstick in a tube, solid deodorant, lip balm and similar solids are allowed. Please remember these items must be solid and not in liquid, gel or aerosol form.
Special Rules on Batteries
The FAA allows passengers to carry most consumer batteries and personal battery-powered devices. Spare batteries must be protected from damage and short circuiting. Battery-powered devices also should be protected from accidental activation. Some batteries have further restrictions, and those are summarized below, and you can find more details in an FAA brochure on the subject.
Batteries Allowed Only in Carry On Baggage
Common dry cell alkaline batteries such as AA, AAA, C, D, 9-volt, and button sized cells.
Dry cell rechargeable batteries such as Nickel Metal Hydride (NiMH) and Nickel Cadmium (NiCad).
Small, rechargeable lithium ion batteries of the types commonly used in a cell phone, PDA, camera, camcorder, handheld video game, or standard laptop computers.
Small, non-rechargeable lithium metal batteries commonly used with cameras and other small personal electronics.
Batteries Allowed in Checked Baggage
Except for spare (uninstalled) lithium batteries, all the batteries allowed in carry on baggage are also allowed in checked baggage. Batteries in checked luggage must be protected from damage and short circuiting, or installed in a device. Battery-powered devices, particularly those with moving parts or those that could heat up, should be protected from accidental activation. Loose lithium batteries are not allowed in checked baggage.
Wheelchair Battery Exception
While spillable batteries are normally not allowed on aircraft in checked or carry-on baggage unless they are part of a passenger's electric wheelchair. Non-spillable wheelchair batteries are allowed if they meet other battery requirements.
Other Airline Restrictions
In addition to the restrictions of the TSA, your airline may also have restrictions on what is allowed on the airplane. If you are carrying an unusual item, or if you thing that an airline may have a restriction, be sure to contact your airline ahead of time, or to contact a representative in the airport. Also, in the event that an airline loses your bags and finds them later, they may have limited Excess Baggage options for getting your bags back to you, especially if you are traveling overseas.
Exceptions for Duty Free Items
If you are traveling internationally and might purchase duty free items, there are exemptions - check with the duty free at your airport when purchasing the item.