A trip to a spa hotel is about relaxing and leaving the world totally behind, so take clothing that is casual, light and easy to slip into. T-shirts and tracksuit pants are ideal. Slippers and plush bathrobes are classic spa attire, but these are usually provided by the resort. Thinking of going for a swim or doing a couple of fitness classes? Toss some workout gear, trainers and a swimming suit into your suitcase too. If your hotel has an on-site restaurant, see if there's any kind of dress code — you may need to bring something fancy to wear to dinner.