Don't worry -- Cathe gives a lot of breaks during her workouts and there is bottled water that the gym provides. I'm not sure on towels (I've always brought my own!). I can't remember if they charged for towels or not (I think they might -- but I'm sure one of the RT coordinators will let you know!) Also, you can rent a locker to keep your things safe, but the last two years, they've always had our stuff placed in a secure room located in the gym (guarded by one of the employees at all times), so you can leave your stuff in that room without having to purchase a secure locker.
Looking forward to meeting you very soon! Julie