There are bike rental places that pick up and deliver to the airport (there use to be one at the airport, not sure if they are still there or not). It's not a lot of time, but it may be cool to get out on a bike for a couple of hours. There are a few beaches near the airport, but not sure about access, etc.

There is also shuttle service to town from the airport if you want to just roam around the town a bit.

The bus company even has real time tracking, so you can see how far away the next bus is.