I've recently made this black bean recipe. You could make it in advance and bring it along:

http://allrecipes.com/Recipe/delicio...os/detail.aspx

I have tweaked it to add in another can of black beans (I use organic with a lower sodium) and a can of Rotel diced tomatoes with chilis and lime. I also only use about a third of the cream cheese that the recipe calls for. Let the mixture simmer until most of the juice from the tomatoes is gone. It's pretty tasty.