At the private island, wear water shoes. Sea urchins lurk in rocky holes very close to shore. If you have your own snorkel and mask, you don't need to pay for private island snorkling; they will provide a free float vest, but I couldn't find where. The water is very bouyant and you can just float (even in 3-4 feet of water) and see fish! Wish I'd thought of feeding them. Great idea.
The Nassau snorkling excursion was great!
In summer you'll need bug repellant for the private island (not when we went in April). Also, we're olive-skinned and still burned while using sunscreen.
Carole