Whereas individual airlines within the United States may differ in luggage regulations, the Transportation Security Administration issues guidelines applying to all airlines. Some of these guidelines include regulations on liquid container size, liquid containment and prohibited items.
The TSA requires bags to be screened at a security checkpoint before being taken onto an aircraft. Further, the TSA prohibits certain items from entering the aircraft as carry-on luggage, whereas some of those same items are fine as checked luggage. As of 2015, these such items include box cutters, meat cleavers, scissors, baseball bats and lacrosse sticks. The TSA forbids other items both as carry-on and as checked luggage. As of 2015, these items include flares, gun lighters, gun powder, dynamite and fireworks.
Liquid items entering the aircraft within carry-on bags are subject to special size and containment restrictions. As of 2015, only certain liquids at a size of no more than 3.4 ounces per container may enter the aircraft, and all liquid containers must be sealed together in one clear quart-sized plastic bag. Passengers must retrieve their plastic bags from their carry-on luggage at the security checkpoint and place them in bins to be screened by TSA agents prior to boarding.
In addition to TSA regulations, individual airlines typically have further guidelines regarding carry-on bags and personal items.