My 17 year old LOVES Downtown Disney.....she loves the music, the stores and Planet Hollywood. It is her must do every trip, which we always accommodate. (While PH is NOT a favorite of mine!)
We had an awesome day on Bay Lake a few years ago tubing....the whole family (and friends!) totally enjoyed it!
Also, at the boardwalk.....the bike rentals (specifically the multiperson bikes with passenger space) are a lot of fun!