I have a little waterproof container that I wear around my neck on a cord. We take a waterproof camera and those come with the wrist strap. Only wear your bathing suit and good gripping shoes or water shoes... you WILL get wet because you are climbing the falls with water RUSHING down over the rocks at the same time, and there are several spots where you are in up to your shoulders and a few places where you slide down into the water if you wish (over your head).
In my waterproof container I put our room key card and money for tipping the guides. Don't need to take anything else... I wouldn't recommend wearing glasses of any kind or a hat... you'll likely lose them. And I leave my 2 piece suit at the hotel on the days we do Dunns River because the rushing water can cause "exposures"
We just left our towels & money on the bus, that's what our driver told us to do. I never saw any lockers to rent, I'm sure they are there I just never saw them or was offered one to rent. We took a waterproof camera, I'm so glad that I didn't take our good digital one.