The Caribbean, as if you didn't know, is a body of water just below the Gulf of Mexico. There are plenty of things to do there. Some of the top choic activities include sailing, fishing, SCUBA diving, snorkeling, parasailing, and jet-skiing. Those of yu from California, don't even thinking about trying to surf here. Unless, of course, you happen to be an insect. If you don't own your own boat, like normal people, try renting from out-of-the-way places. Bargains and lower prices are more likely to be found here. Then, get some friends and try some of the above.
I suggest off land. The absolute, positive best place to stay in a tropical area is on a boat. I suggest a catamaran with a cabin in the middle, not just a tarp or sheet of plastic. Anchoring places can be a little tricky. If you plan on visiting some land that evening or early morning, rent a space on a dick or marina. If there is no hurry, always stay out anchored in the harbor (away from land). One can pull up and rent a slot for half as much for just the day time, as opposed to the night-long rentals.
If you are scared of water, get seasick easily, or are too stubborn to follow my earlier advice, NEVER stay in well-advertised hotels. They charge about 100-200$ extra per night for "accomodations". It's all a load of bull. They lure you in with good ads, and then use the extra $ on more ads and more profits. The best hotels are the small cottage-like places near marinas. If, however, you have a discount or free invitation to a really nice place, feel free to go right ahead. It would take an itiot to turn that kind of an offer down. But these people still get cancelations, because there is still a large percentage of itiots left here.
Always go to Key West. There is tons of stuff to visit. While there, don't miss...
Also, some of the best SCUBA is found in the southern area of this sea. The farther south, the clearer the water. The best I've seen, however, is at Grand Camen. Stay at Hell, the city, and spend a week in paradise.
Never ever skip the Virgin islands or Jamaica. They are both great places to visit and have tons oif wildlife to see. Sometimes you'll even see the huge iguanas native to both. Although expensive, these are some of the best islands in the Caribbean.