Be aware of restrictions on the size and number of bags you may bring onto your flight. Certain discounters (including Spirit Airlines, Ryanair and easyJet) now charge a fee for every checked bag, while many other airlines have been lowering the maximum permitted weight limits for checked luggage. While most airlines allow passengers one carry-on bag and one personal item, travelers headed to or passing through the U.K. may only bring one small bag through airport security checkpoints (and the size restrictions are rigidly enforced). Your best bet is to check your airline's Web site as well as the TSA Web site before every trip to be sure your bags are compliant with the latest rules and regulations.