I am a cast member in Richmond Va and i got to go on the criuse the first weekend in Feb.
When you get ready to set sail they have a sailaway party at every port. There really isn't a lot to do on the boat(movie theater, arcade, pin pong tables and shops, comedy club at night, whole deck called Oceaner's Club for childre and a teen club).
When you arrive at Castaway Cay you are able to rent snorkel equipment for $25 and inner tubes for $6. You can also take your own just make sure you have a lifevest(Disney requires it.)
If you decide to go snorkeling there is a trail that you can follow to see the sub and parts of a shipwreck. Make sure to look for the Mickey that is fishing near the buoy. Also the fish group up all around you like you are one of their own so if you don't like fish i would not suggest doing the snorkeling.
Even though there wasn't a lot to do it was a fun time that i would recommend to anybody.
Also if you are looking to save money book your trip really early. A cruise line cast member told us that the prices go up as the boat fills up.(i.e. if you book about a year in advance you will pay less then if you book six months in advance).
If you are looking for a secluded place to go, go out on deck four under the life boats. When I went there was never anybody else out there with my family and I.