Baobab juice
Palm Wine
Is juice from palmtrees that is collected and fermented. it is used as a kind of wine by the locals, and you may get a chance to try it if you go on a tour to rural gambia.
Julbrew
Gambia's own beer, Julbrew (http://www.julbrew.gm/) is worth a try. It's made by Banjul Breweries, who also make soft drinks.