For our family of five for the 7 day WC in August, we used 2.5 cans of Coppertone Wacky Foam SPF 70, 2 cans of the Coppertone SPF 50 Spray, and 1.5 bottles of Neutrogena SPF 70 Beach lotion. We spent most of our port days out in the sun and also in the water so we made sure we used ample sunscreen. We applied it before leaving the ship, and reapplied at least twice during the day. We managed to avoid burns completely.
I was shocked, though, that even with slathering lotion all day that we all got some tan. I'm pretty fair skinned, and even with all that sunscreen I got a tan. That Caribbean sun is intense!