In the first half of 2012, U.S. airlines raked in $1.7 billion in baggage fees, the largest amount ever collected by the industry in a six-month period. These fees, which are tacked onto an optional service that was mostly free years ago, are both costly and endlessly complex. But with a little know-how and some planning ahead, you can beat 'em. Here are seven smart strategies for avoiding expensive airline baggage fees on every trip.