I am betting an original owner added that to hold.....something. It is not ever going to be known exactly what. It was not likely original from the factory, so there would be no way of knowing without knowing or being a direct descendant of the person who put it there. I would use it to hold both my beers whilst frying sausage and eggs on the stove.
I think they camped in the swamp and that held two cans of Deep Woods Off. And that is probably as good a guess as any, it is not real old judging by the Velcro straps and I am certain it wasn't factory.