This was not on the ship, but the coolest free thing for me was scoring a quiet hammock under a shady palm tree on
Castaway Cay with no one else around but my own family. I had kids with me, so I didn't go to Serenity Bay, but I got the tip to walk all the way around the family beach (with the provided FREE baby jogger!) to the very end by the bar. There are two hammocks there and no one around for a very good distance except my favorite people to see in this instance...bartenders! They regularly trooped by with everyone else's drink orders. This is the only place I indulged in paying the Disney price for alcohol and it was worth every sip! Swinging in the shade with a sleeping child and a fruity drink was the perfect end to the trip.