As you're likely to be spending much of your time at the hotel in a fluffy robe and slippers, you won't need to take too many belongings. Besides casual, loose-fitting clothes to put on after your treatments, essentials such as deodorant and a toothbrush should be at the very top of your packing list. Of course, if you plan to use the hot tub or pool, or engage in exercise sessions, toss a bathing suit and some workout clothes in your bag as well. Finally, leave the electronic devices behind and bring a good book instead. It is a relaxation break, after all.