hi vicky
i never did any shore excursions arranged by the cruiseline. either i booked one in advance-check out www.cruisecritic.com -there is plenty information on the boards about all the things to do at your stops. or you just go out the port-there are plenty of taxis and tour operators who want to take you out and show you what you like to see. and all of them are much more cheaper than going by a tour booked via the ship. and another advantage is, you get to see what you like and need not to wait for all of the others of your tour
i did the same trip a couple of years ago-but just went out for beaching-so i cannot give you many tips what to see and to do
but if you are in st lucia-don't spent money&wasting time of seeing the pitons with a boat trip-because your cruiseship will pass&stop there anyway for taking some nice pictures
if you have any other questions just ask