Ambers idea of swimming in the lake! magicswim- an inflatable pool for boating (tiny holes in the bottom so lake/ocean water fills the pool without the fish and stuff) Perfect because all of the "stuff" is gross.
Adding stumps and other balancing elements creates a sand play area that is so much more than just a sand box. This appeals to a much wider age range than a box of sand. Can become a fire pit when the kids get older.