Most ports have their own beer at very reasonable prices (usually $1.00-$2.00). Caribe is a popular beer as well as Red Stripe. Most mixed drinks are reasonable ($3-$5). Some ports have rum tasting so you can buy their brand of rum. Enjoy your cruise!
We got some wonderful caribbean flavored rum in St. Martin... (Even came in a decorative bottle that was hand painted in the shape of an island woman) I think we paid around 7.50 for each. Tasted great, but wanted the bottle more than anything. Found it right as we were coming back to the ship... Make sure to barter..... we got a better deal since we haggled and purchased more than one.