I read a bunch of posts for the snorkling at CC... I have done it on both my past trips, and you don't have to rent your equipment until you board the ship...
I did the snorkel trails next to the family beach, and I saw some sea life, but it was like sea life hog heaven at the adult only beach. I saw this MASSIVE black sting ray.. it had to be like 4 feet. I saw several other sting rays, lots of fish, crabs in big conk shells. It was awesome, and the water isn't crowded, and it's so peaceful, really like you are snorkling on some deserted island. Then I got a float, and spent the next two hours floating around the adult beach, reading a book.. oh it was heaven.