This means that if you’re going to pick up a bottle of water or soda for the plane, be sure to buy it and stow it in your carry-on after security, not before. (Don’t be that bleary-eyed traveler who shows up at an early-morning checkpoint with a cup of coffee you just bought, only to have to throw it away.) Note that there are a few exceptions to this rule, including essential medications and food for infants or children.