Hint: we always take clean towels from the hotel pool the day before and bring them with us to TL or BB. When we come back, we drop the used towels in the pool's towel bin.
Towels are $1 apiece. You get them at the same place you get locker keys. There are CMs stationed near the water parks' entrances pointing you in the direction of the lockers, so you'll have no trouble finding them.