Beaches - you are never far from a great beach and this includes the capital Bridgetown. Carlise bay is the closest best beach which is also chosen by the cruise ships. It's a fun busy beach experience if that is you. The scuba dive operations are centered around here too.
Crane Beach and Resort - A very nice lunch at the cliff top and TOP resort allows you to recharge after having fun in the waves at Crane Beach.
Fish Friday - An evening of fun and food dancing and drinking out in the open - read this Oistins blog post to learn more.
Cave - the Harrisons Cave system is a worth point of interest if this is your thing. If you got a bit too much sun it might be a good tip.
Nightlife Mojos - Akra Beach area and St Lawrence Gap.
If you're wanting to escape the cruise ship for a bit then I would recommend walking into Bridgetown - take your time visiting such curiosities as art shops and the cigar factory which is close by to the ship : walking towards town from the port with the sea on your right look left and you will see a nice manicured set of shops
In here you will find some expert cigar makers who are happy to answer your questions and plenty of shopping opportunities. Keep going into Bridgetown and if you took your swimmers and snorkle set enjoy the later part of your stay on the beach. Many head for the beach bar aptly named the Boat House that does a whole package of all the things you need.