Yes! USD is equivalent to the Bahamian dollar! The island accepts USD. You should have enough cash on hand to pay both ways for the airport taxi ($5/pp), water taxi ($5/pp), extra for tipping helping with bags, etc. A cash machine or ATM can be found at the RBC branch at the top of Dunmore Street (The Bahamian dollar is pegged to the US dollar, and both currencies are accepted throughout the island.)
Sunscreen can be found at the Tip Top Store, The Valentines Dive Shop & the Piggly Wiggly Supermarket. The Piggly Wiggly is in the heart of town! There are a few other places to grab snacks, including Captain Bob's, which is up the hill. If you are staying in an airbnb or hotel and want to guarantee certain foods, you can place a provisions order ahead of time!
Accidents do happen! If you do need emergency contacts: The Clinic + 1 242 333 2227 Harbour Island Police Station +1 242 333 2111