WE'VE ALL BEEN tempted to skimp on our luggage purchases. Especially if travel is an occasional event, it's hard to justify spending good money for something that'll sit in your closet for most of the year. Think of it this way: Buying a dependable bag is buying peace of mind. A few yards of zippers and either hard plastic or nylon are the only barriers between your bag and the belly of an airliner, the conveyor belt of a baggage claim, and the trunk of a car. Make one thing easy on yourself and bring good luggage that's lightweight, rolls easily or fits comfortably on your back, and won't split open on the way to your destination.