I have a lightweight Goretex parka that I sometimes use, but really, the rain squalls pass by quickly, so you don't need to take up luggage space with foulies.
I actually found a thin, longsleeve knit polypropylene shirt to be most useful, the kind sold in outdoor stores as "thermal underwear". It can get a little chilly standing at the wheel
in a squall. You can also use it for snorkeling to keep the sun off your back.
Most visitors don't bother with special vaccinations, but here's a link you can check out...
Caribbean - Region - Travelers' Health - CDC