We have done the stingray tour twice in Cayman islands. You will leave your stuff on the boat that will take you out to the sandbar. The boat will stay with you the whole time so your stuff will be safe.
As for ocho rios we have been there twice. We usually do the dunns river falls and that's it this is not a nice island especially to walk around town. They are always coming up to you offering you drugs. I really don't like any island in jamaica.