As you'll probably spend quite a bit of your time at the hotel in a robe and slippers, you won't need to bring a whole lot with you. Besides casual, loose-fitting clothes to slip into after your spa treatments, essentials like underwear and a toothbrush should be right at the top of your packing list. Of course, if you intend to make use of the pool or hot tub, or get physical with an exercise class or two, squeeze a swimsuit and some activewear into your bag as well. Finally, leave the laptop and smartphone at home and take a good read instead. It is a relaxation trip, after all.