Please keep in mind, it is over an hour to drive to Disney form the port. At best, you'll have about 4-5 hours to spend at the park. If you're a Disney fanatic, go for it. Otherwise, the NASA tour is excellent and only a few miles away.
Nassau is bustling, and only a few minute's walk from the ship. There are a variety of stores- from T shirts and hats, to formal wear. The Bahamas International Film Festival was going on, and we briefly considered taking in a movie! There is plenty to do in Nassau, whether you book an excursion or not.
Unless you book an excursion, you won't really see Freeport. Instead, you'll be treated to the local Senor Frogs, and a straw market. I suppose there are some good deals to be had, but we quickly re-boarded the ship.