Mel Fisher's museum is a must do for tourists. There is a little aquarium too - across the street. Get some frozen key lime pie on a stick at the Blonde Giraffe. Get a cheeseburger at Margaritaville. You'll be in tourist heaven after all that!
Just be careful with the t-shirt shops and an offer to do a "custom" design. You can easily end up with a $50 t-shirt at some of the shops if you aren't careful.