Pour the 4 cups of cheerios and 4 cups rice chex into a turkey roaster or a large sheet pan.
Preheat the oven to 275 degrees.
Over low heat, melt the butter and brown sugar.
Pour the brown sugar mixture over the cereal and gently stir to coat.
Bake for 45 minutes, stirring every 15 minutes.
While the cereal is baking, pour all the add-ins into a large bowl and gently combine; set aside.
When the cereal comes out of the oven, let completely cool, about 30 minutes or so.
When the cereal mixture is cool, pour in the add-ins and gently stir to combine.
Pour the mix into your favorite serving dish and enjoy!