Preheat the oven to 275F degrees (convection oven works better).
Melt the butter in a medium saucepan over medium-low heat. Add brown sugar, corn syrup and soy sauce and stir until the brown sugar dissolves.
Pour the rice Chex, Cheerios, Bugles, pretzels and nuts into a large mixing bowl and mix through. Drizzle the syrup a little at a time over the cereal and mix well. Continue adding syrup until all of it has been added and the snack mix is evenly coated.
Put the mix on two flat sheet pans and sprinkle with a little kosher salt and cracked black pepper. Bake for 1 hour, stirring the snack mix after 30 minutes, rotating the pans half way through. Sprinkle with a little more kosher salt and cracked pepper one more time half way through.
Remove from the oven and let cool completely. Add the candy corn and/or M&Ms after it cools.
