Itchetucknee is very good, a day of entertainment, and you don't have to lug the tube all over creation, as you can drop the tubes, drive to the bottom, and get a bus ride back to the top of the run.
Don't forget, you're only about an hour and a half from nice beaches. Crescent beach is a nice somewhat out of the way white sand beach (not much surfing in Fl, no waves), and St. Augustine is pretty neat for seeing the Spanish presence in historical Florida. The many alligator farms (one or two in St. Augustine) give you a chance to see the local wildlife in a closed environment, and yes, most have a resident "idiot" who will put his whole arm (or head if really an idiot) in between the jaws of a gator, and afterwards tap the mouth to get a nice snap shut, accompanied by a sound similar to homerun baseball hit.
BTW, Crescent has a small entry fee to drive on the beach from Memorial Day to Labor day. At other times, it's free, but the beach is not kept up as well, and you can get stuck if not careful. Be sure to keep your drive wheels nearest to the water/driving area when parking.