This I guess depends on your preference. You can leave and come back to the ship as many times as you like. Example, leave in the morning and go ashore, come back for lunch, then go back ashore in the afternoon. However, be advised you must be back onboard 30 minutes prior to sailing. They will not wait for you unless you are on an excursion that you booked through the cruise line.
As people stated, there are plenty of choices in your ports of call. The BBQ lunch in Coco Cay was great! Call me old fashioned, but I just went to the Burger King in Nassau, had the BBQ at Coco Cay, and went to the Johnny Rockets on the ship when I was in Key West.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)