RELAX!!!! Have a nice dinner and a drink (if you choose). You have arrived and there shouldn't be anything left to do.
However, if you arrive early enough (and have others in your party who would like to split the cost) I would suggest renting a car for the day at the Radisson and driving to the Kennedy Space Center. We did this on the day we got off the ship (since they kick you out of your room by 8am) and were at the KSC by 9:30am. It was absolutely fascinating and worth the $28 adult fee.
Other than that I would suggest you just make sure you have a book or magazine to read on the cruise. ENJOY!