As you're likely to be spending quite a bit of your time at the hotel wearing only a robe and slippers, you won't need to bring a whole lot with you. Besides casual clothes to put on after your spa treatments, essentials such as a toothbrush and underwear should be right at the top of your packing list. Of course, if you intend to use the pool or steam room, or enjoy a few exercise sessions, toss a swimming suit and some activewear into your bag as well. Finally, leave the laptop and smartphone behind and bring a good book instead. It is a relaxation escape, after all.