If the weather’s nice, I’d say just hang around on the beach. If you want something a bit more active, Ron Jon’s rents bikes, and in about 2 hours you can take a leisurely bike ride either up and down the beach or across the causeway to Merrit Island. For a full free day, Kennedy Space Center is nearby, and it doesn’t matter how the weather is. (And you can’t beat their IMAX movies for cheesiness…)

(Incidentally, I used to spend 2 weeks every year in Cocoa Beach for crew winter training, and it’s definitely a nice place to just sit and relax when you don’t have practice, I think)

If your interested…NASA is there with tours, etc. But hanging out on the beach is one of the main reasons FL exists ;)