Hi Challon, welcome to CruiseReviews! Congratulations on your upcoming cruise. I LOVE the southern itineraries. St. Kitts is a pretty island, I second Jim's recommendation for Brimstone Hill. I also enjoyed watching them do the Batik.
St. Lucia is one of my most favorite islands. The locals are so friendly. The last time we were there we went to Pigeon Island. It was a really beautiful area, including the fort and the lookout was gorgeous. The snorkeling at the pitons is really good.
What are some of your interests? It might help us to make some suggestions to know what you enjoy doing.
Hope you have a marvelous time!