Hmmm, two things come to mind. First, you could rent a car for the day and then head over to the beach and shopping areas in Ft. Lauderdale. Stick the bags in the trunk and off you go. The car rental companies are just a short distance away (as is the airport)
Second idea, if you are a sun person, grab a taxi to the Marriott (close by) check your bags with the bell man and hang by their pool. They have a great lunch bar/cafe that you can wear your bathing suit to and when it comes time to go to the airport, change in the fitness center.
OK, third idea. Drop your bags with the bell man at the Marriott and then climb aboard the water taxi and take a tour of Ft. Lauderdale's Inter Coastal. We did this once and were able to buy tee shirts good for 2 for 1 drinks at the various restaurants and bars along the way. They cross out their bar on the tee shirt when they searve the drinks. It is very fun if you want to party a little bit while sightseeing