we have a swimming Dora, we have foam letters that stick on the wall when wet, ummm different sized plastic balls that float and different cups to put them in, marine plastic animals (like a farm set but stuff like whales/squid/fish), from Kmart I got a shower thingy that attaches via suction cup and you push a big button and the shower squirts (it's a bit useless IMO).
I just keep them in a basket in the laundry and rotate them from time to time.