As you're likely to be spending a fair amount of your time at the hotel in a robe and slippers, you won't need to bring a lot with you. Besides comfy, loose-fitting clothes to change into after your treatments, personal items such as underwear and toiletries should be right at the top of your packing list. Of course, if you plan to make use of the resort's swimming pool or try out an exercise class or two, throw a swimsuit and some gym attire into your bag as well. Finally, leave the laptop and smartphone behind and bring a book instead. It is, after all, meant to be an escape from the real world.