There is nothing to do at Freeport Port. There are some flea market type shops but nothing serious here. They shut down when the Carnaval ship leaves or open late and close early when only the Celebration is in Freeport.
Take the $10 round-trip taxi to Port Lucaya for shopping, rum, beach access, and fantastic $11 conch salad made to order at the end of the free beach access.
Or, in advance, contact Deadmans Reef AKA Paradise Cove (Google it). They will pick you up at the ship and you can spend the day on the beach, snorkeling, and kayaking then return you to the ship whenever you want.