Did you know that British Airways (BA) has a number of Fifth Freedom Flights in the Caribbean? Well I did not until I read this Flyertalk thread.
Here is the overview:
Now as we know the BA miles (called Avios) are a great currency to redeem for short Economy flights. BA makes that a bit hard sometimes as it adds high fuel surcharges but for those short ‘Fifth Freedom’ flights NO fuel surcharges are applicable.
Take some time and look up these airport codes- I have built a sample itinerary with each leg costing 4,000 (low season) or 4,500 (regular) Avios.
There are a lot of combinations you can run – it depends on how many flights you are able to digest and how many Avios you have saved up.
I found availability to be quite good – most routes have a couple of seats available.
Now all you would need to do is the flights from and to your home airport to the beginning and end of your island hopping.
American Airlines has a lot of flights to many Caribbean airports (mostly from Miami) but award availability can be an issue. If it is available you can pay with Avios as well. Sometimes US Airways (from CLT) has good availability on Caribbean flights as well.
However American has some deals (like the one below) when paying cash many times. I found this using Kayak.com.
United and Delta also fly to Caribbean – as well JetBlue from New York.
Another alternative is to use Airtran with SouthWest points (though there are much fewer destinations).