Prohibited items for carry-on luggage include sharp objects, guns and firearms, martial arts and self-defense items, explosive and flammable items and disabling chemicals. A number of tools and sporting goods items are also banned. You can find specific details on individual items along with a list of other restricted dangerous items on the Transport Security Administration website.
New restrictions for quantities of liquids, aerosols and gels allowed in carry-on luggage were introduced in 2006. Passengers are allowed one quart size clear plastic bag containing up to 3.4 ounce bottles. If you are in doubt, place liquids in your checked-in luggage. Exemptions are made for prescribed medications, breast milk and baby formula and food.
Restrictions on carry-on luggage also apply to all children. Children's items, such as diaper bags, blankets and toys, must all be checked. Items such as strollers, baby carriers and car seats must all go through the X-ray machine. You should not be asked to do anything that would separate you from your child while baggage is being checked.
TSA has developed guidance on "checkpoint friendly" laptops to avoid delays when carry-on laptops have to be removed from their carriers for inspection. To check inside of the computers, security officers need an unobstructed view of the machines as they pass through X-ray machines. Laptop bags should have a laptop only section that can be laid out flat for X-ray. Checkpoint friendly bags will not have internal or external pockets, metals snaps, zippers or buckles inside. There should not be anything else in the laptop compartment.
The weight of carry-on baggage and the number of pieces allowed varies among airlines. Some airlines specify that baggage must fit in overhead lockers while others have different rules on whether items such as laptops and handbags are allowed in addition to other pieces of baggage. You should check individual airline websites for their specific restrictions or use the dpsoftware website as a tool to compare restrictions among different carriers.