Prepare your campfire or camp stove to create a bed of coals or a stable low flame. For a 12-inch Dutch oven, you'll want about 6-8 hot coals underneath and 10-12 on top for a 350°F oven.
Place the Dutch oven on a heat-safe surface. Pour both cans of peaches (undrained) into the bottom. No need to stir.
Sprinkle the entire box of dry cake mix evenly over the peaches. Do not stir. This is key — the cake mix will absorb the juice and create the topping.
Pour the lemon-lime soda (or water) evenly over the cake mix. Do not stir. The soda adds bubbles that make the topping light.
Scatter the cinnamon and butter pats on top if using.
Put the lid on the Dutch oven. Using a lid lifter or tongs, place the hot coals on top and underneath. If using a camp stove, set the oven directly on a low burner and check heat after 10 minutes.
Cook for 30-40 minutes, rotating the oven and lid a quarter turn every 10 minutes for even heat. The cobbler is done when the top is golden brown and the edges are bubbly.
Carefully remove the Dutch oven from heat. Let it rest for 5 minutes — the filling will thicken as it cools. Serve warm, straight from the pot.
