there is free water and Princess provides a lunch there with melons, pineapple, chicken, hamburgers, desserts, beverages,etc.
There are a couple stores to shop in.
Get one an early boat to get to the island as you want to get one of the spots that has sun which is all the way down the pathway toward the end where the food is.
As to the rental stuff it is right at the dock.
Prices I don't really recall.
If you take some dollars you can go out the gate to some small vendor shops but there isn't much there to see so don't waste your time.
Leftover food you can throw in to the fish and see them swarm off the
small pier that is there by the picnic area.
I took my own snorkel stuff. You can buy it for $40 at Costco and use it the whole trip. However, most snorkel tours will provide equipment for you.