We rented last time and purchased our own prior to our upcoming trip because we wanted full face masks. We'll just grab vests before we head into the water. We have mini fins and if they seem like they aren't enough, we can always rent fins, too.
We really enjoyed snorkeling. We say a ray, a sea turtle and a lot of fish. I laughed so hard as my husband snorkeled past me while I was taking a break above water and I could hear him saying "Here, fishy fishy" out of his snorkel.