Free or not too expensive things to do?

My Fiance and I are staying on my parents' "property" at Frenchmen's Cove (Marriott). I haven't been since high school (10+ years ago) and my Fiance has never been at STT. Our wedding is approaching leaving us with minimal travel funds. What are some fun and low-cost or free things we can do? We love outdoor things, and the beach but I can only do the beach for so long. My passport is still being processed and may not be back in time to visit BVI.