Don’t let runners shame you; walking is fantastic exercise. Add in a heavy pack plus a few mountaintop passes and it becomes a great weight-loss activity. Steve Silberberg runs Fit Packing, a company that helps clients slim down through multi-day backpacking trips. He says that hiking with a loaded pack burns more than 4,000 calories a day. By the end of his seven-day trips, most clients have lost about five pounds — and usually gained some muscle too.