In a skillet over medium heat, sauté the onions and celery in the butter until soft but not brown.
Combine the cornbread and white bread cubes with the onion and celery in a casserole dish.
Preheat the camp oven to 350 degrees F (175 degrees C).
In a bowl add the 2 eggs, then gently beat. Add the sage, poultry seasoning, and pepper and whisk again. Finally, add the chicken broth and give one last short whisk to combine.
Pour the stock mixture over the bread mixture and leave it to sit for 5 minutes for the bread to absorb the fluids.
Stir the casserole to redistribute the moisture then place it in the camp oven. Bake for 45 minutes. Serve hot.