As you're likely to be spending much of your time at the hotel in slippers and a robe, you won't need to take a lot with you. Besides comfy clothes to slip on after your massage and spa treatments, essential items such as underwear and deodorant should be at the very top of your packing list. Of course, if you plan to use the pool or steam room, or sweat it out at an exercise class or two, toss a swimsuit and some gym gear in your bag too. Finally, leave the electronics in your office and take a good book instead. It is, after all, meant to be an escape from the real world.