We took a taxi from the port to Magen's Bay. We spent the day at the beach and it was amazing. Anyone who likes the beach/ocean should check out this beach - definitely a must-see! We took a look through the shops at the port on the way back to the ship but didn't make any purchases.
The port terminal has free WiFi - lots of passengers took this opportunity to get "online". There are several stores to shop at for souvenirs right at the port.
We took a taxi from the port to downtown Bridgetown. We were personally very overwhelmed by how busy it was. There are lots of stores, people, traffic, etc.
We quickly followed others to The Boatyard - this is a restaurant/bar/private beach area right off downtown. As we were tired of the cruise ship food, we had some very good seafood and wings here and lots of drinks. The cruise ship crew tend to frequent this place. We spent the rest of the day lazing around on the beach. If you're on a budget, this was a nice way to spend the day in Barbados.
This was the only port that we "splurged" at. We purchased the Catamaran excursion from Carnival. Honestly - it wasn't worth the money we spent. This may have been due to the bad weather that day. You get to see a bunch of small fishing villages and The Pitons. Nothing "wowed" us on this excursion. If you do decide to go - just being on the boat itself with unlimited rum punch can prove to be great fun :) The cruise terminal had lots of shopping. We bought some conch fritters from the restaurant on the second floor - very yummy!