Place a cast iron skillet over the campfire flames, and heat up. Add the bacon and fry until crispy.
Add the bread to the skillet, so that it fries in the bacon grease. Once crispy and golden, remove the skillet from the heat.
Toast the marshmallows in the campfire flames.
Spread 2 slices of bread with peanut butter, place bacon on top, and finally add the toasted marshmallows before sealing with the second piece of toast.