As you'll likely be spending a decent amount of your time in a robe and slippers, you won't need to bring a lot with you. Besides casual clothes to change into after your massage and spa treatments, basics like a toothbrush and underwear should be at the very top of your packing list. Of course, if you intend to make use of the pool or get physical with an exercise class or two, squeeze a bathing suit and some sports gear into your bag as well. Finally, leave your electronic devices in your office and take some light reading instead. It is, after all, meant to be an escape from the real world.