You should have a great time with this geocache boating, kayaking whatever you are doing. There are trail all over the island there is a cool pirate ship there and some little Florida cliffs on the other side of the island.
Yes there are tree roots there were I slipped through one be careful. The people at spoilislandproject.org said to please practice some CITO.
you are looking for a small blue rectalgular container big enough to fit some very little things and a log book every geocache should have something inside) there is a pen but just in case BYOP.