Pack a swimsuit, toothbrush, meds,C cards/log, mask, and reg in your carryon. There is a very good chance none of your luggage will arrive when you do, especially if you have a layover on the mainland. One in our party last year has been 5 times, and has received all of his luggage twice. It all eventually arrives, but maybe not until day 3.
The item I was most thankful I brought was powdered gatorade. We were happy to have it, as nearly everyone in our party came down with the traveller's diarrhea. Nothing debilitating, but it did stick around for a day or so. Gatorade is expensive there. So is Immodium. bring plenty.
Last year, i way overpacked as far as clothing goes. When they say "Casual Attire" for the resort, they mean it. I even wore pyjamas to dinner one night. Do bring one more towel than you think you need.
We used Deet and cactus juice, and both seemed to work equally well. Spray yourself as soon as you step out of the room. Keep your door closed.
We brought 700 cash for 2 of us and had some left. We did all of the dolphin things, and won't be doing them again this year. They were fun, but I don't want to spend the money again. They accept credit cards at the desk, and I think you can even get cash if you don't bring enough. I think we tipped the boat captain and DM $10/person/day, plus a little extra.
The food quality was good to excellent. Bring some snacks for the boat. the little snack shop is pricey. We had granola bars, power bars, and dried fruit/nuts that we ate nearly all of. I think I am going to pack a soft sided cooler this trip to have on the boat.
We brought our own hard liquor to avoid having to go into town. We packed it in plastic flasks and listerine bottles and had no problems.
We had a fantastic time, so we are returning this year. It was a very easy vacation - we did nothing. We did set up our own gear, but they will do it for you if you are that lazy on vacation. You have to sign up for the dives you will be going on, and they will put your tank in your spot for you. Pick a good spot on the boat. It's yours all week.
Now I want to go pack!!!