The size of carry-on luggage is determined by the International Air Transport Association (IATA) to be a maximum of 22 inches tall, 18 inches wide and 10 inches deep, including any side pockets, handles and wheels. Since this is an international regulation, airplanes are actually built to fit this size of carry-on luggage. Airlines may restrict the size and weight of the carry-on luggage further.
The TSA sets rules on what may be transported on board an airplane. This is for security reasons, to minimize the risk for travelers of both malicious acts by other passengers and accidents due to dangerous materials. Generally, restrictions apply to weapons such as guns and knives, but also anything that can be used as a weapon, such as knitting needles and fry pans. There are also regulations regarding gas canisters, explosives and liquids.
The amount of liquids and gels that can be taken in the carry-on luggage through the security checkpoint is restricted. This does not include any goods purchased after the security checkpoint, since goods sold in the airport have been pre-checked by the airport security. Liquids and gels include toothpaste, skin cream, shoe polish, and anything that is not a powder or solid.
The TSA created the "3-1-1" rule for how much liquid can be carried on board, and this has been internationally accepted and implemented by most other countries. The rule is that each bottle of liquid or gel can be a maximum of 100 ml (3.4 ounces), all bottles must be placed in one quart-sized clear plastic bag and there is only one bag allowed per traveler. It is possible to check additional liquids, and there is an additional allowance for babies and medication, but this has to be declared to the TSA agent at the security checkpoint.
Laptops can be brought on board the airplane as carry-on luggage. Airlines do not recommend that they be carried in checked luggage. Laptops have to be controlled at the security checkpoint. The TSA has started certifying "security-friendly" laptop bags, where the laptop does not have to be taken out of the bag to be X-rayed. If such a bag is not used, the laptop has to be taken out to be X-rayed. Other types of electronics, such as music players, are normally allowed on aircraft. However, anything that radiates radio waves, such as mobile phones and remote controls for toys, have to be shut off during travel--although some airlines have started to allow mobile phones. For security reasons, using any electronic equipment on board is not allowed until the airplane has reached the cruising altitude.
It is possible to bring a wide variety of goods on a flight, such as deer antlers, throwing javelins and hand tools. Normally, airlines require that special items be carried in checked-in luggage and does not accept any liability. However, the rules are set by the airlines and can vary. It is best to check with the airline before bringing any special goods.
The TSA prohibits loose lithium batteries in checked luggage. Generally, batteries have to be taken out of anything battery-powered before it is put into the checked luggage, and loose batteries taken in carry-on luggage. However, here as well, each airline can set its own rules above what the TSA requires.
