I've gone to the Bahamas in spring, summer, and fall and basically packed the same.
I always take summer clothes but I think in fall I added long pants. I always take a cardigan sweater (or two) to wear over a sleeveless top or dress even in summer (because almost everywhere has air conditioning).
An umbrella might be a good idea too. I was just looking at a video from our Thanksgiving 2000 visit to Paradise Island and I saw that it rained the first two days.
Don't forget batteries for the camera/video recorder. If the batteries are regular kind, the recharable ones aren't very expensive (you can buy an inexpensive 4-pack with the charger at WalMart).
wouldn't you just love to beeeeeeeeeee me? "-)