If you have some time to kill in the area then you can pop over to the Bayside Marketplace which is a busy open-air mixture of shops, restaurants, and various entertainment. There is also a 90 minute boat tour that departs from the marketplace that will give you a tour of the port, views of Miami skyline as well as waterfront mansions, and more. If you don't want to leave the terminal there is duty-free shopping you might be able to enjoy depending on your cruise.
If you are looking at killing more time then there is a hop-on/off bus that departs from Bayfront Park's Central Station and makes various stops in Miami and South Beach like Vizcaya, Biltmore Hotel, Coral Gables, and Little Havana. Another option would be taking the elevated Metromover to downtown Miami to do some shopping.