Yep, been there so many times there's only one thing we want to do; go to the beach and relax! We take the bus to Calico Jack's on 7-Mile Beach. They have a great beach, good burgers, cold beer, and tents for plenty of shade. Plus, right next door is Red Sail Sports where you can rent jet skis, sail boats, go parasailing, etc.
But if you're into snorkeling, 7-Mile Beach is not the place to go - it's all beautiful white sand. Fish hang around coral reef because it provides food and shelter. So if you want good snorkeling, there's a couple of great sites right near downtown.