When it comes to carry-on luggage, one of the most important rules to keep in mind is that it needs to fit either in the overhead bin or beneath the seat in front for you for safety. Adhering to the airline’s carry-on size requirements will ensure this. As for what you can pack inside, check with your airline and TSA.gov for a complete list of prohibited items, but these include firearms and ammunition, lithium batteries, pocket knives, flammable products, and other hazardous items. If packing liquid, gel, or aerosol products in your carry-on, be sure that their containers clock in at 3.4 ounces or under, and that said containers all fit in one quart-size, clear sealable bag. (You don’t want to have to throw away that expensive toner at security!)