My wife and I are on Ambergris Caye for our second trip right now. Both times we had provisioning done for us by Mata Grande. You can order what you want online ahead of time and it will be delivered to your room and waiting for you when you get there. (that means you will have cold Belekins in your fridge waiting for you).

We have ordered the bare essentials pack which has rum, vodka, beer and some sodas along with groceries. As I said, it's not cheap but I think you save quite a bit over getting all your drinks and food from resorts or restaurants. You also get to play "what in the hell can I make from this." This moringings scrambled eggs with calabrese salami was awesome.

Have a great trip.