There is lots to do in Barbados... I have been on vacation here before and if you are looking for a unique excursion I recommend swimming with turtles. Barbados is one of the few nesting grounds for the leather back turtles and a catamaran ride and swim with them is always a nice day. Be for warned sometimes these excursions can get a little crouded. You will see a turtle but you won't be alone.
There are also several "Shipwrecks" which have been placed there for SUPER snorkeling
Another great spot for a fun day is the boatyard. It is what they call an "Adventure beach" Google it, they have a website. It costs $15 to get in, lockers, food and water rentals are extra but they do have a water trampaleen a rock climbing wall in the water and an all in all crouded but fun enviroment.
There is some shopping around town a potery shop and such but I would hit the beaches for some great snorkeling or take a tour to see some turtles.