Mix together the cinnamon and 1 tablespoon of the sugar. Set aside.
In a medium (10-inch) cast-iron skillet, combine the grapes and berries with 2 tablespoons of the pancake mix and ¼ cup of the sugar. On a camping stove, cook over medium heat, stirring often, until the mixture begins to thicken, 10 to 15 minutes.
While the fruit cooks, combine the remaining 1½ cups pancake mix and the buttermilk in a small mixing bowl. Stir until it forms a sticky dough, adding a splash of water if needed. The dough should be thick enough to hold its shape on a spoon.