Most airlines won't allow carry-ons taller than 22 inches and even if you're checking your bags, you should try to avoid using a bigger suitcase. "Over 26 inches, it's easy to pack over 50 pounds," McAlpin says. "The bigger the bag, the easier it is to throw too much stuff in." Find a conveniently sized back and keep using it until you understand how much it can hold without incurring extra fees.