Given you'll probably spend much of your time dressed in just a robe and slippers, you won't need to take too many belongings. Besides comfy clothes to change into after your spa treatments, personal items such as a toothbrush and underwear should be at the very top of your packing list. Of course, if you plan to use the pool or engage in exercise sessions, toss a swimsuit and some activewear in your bag as well. Finally, leave your electronics at home and take something light to read instead. It is a relaxation escape, after all.