Combine crispy corn and rice cereal, honey graham cereal, peanut butter corn puff cereal, popcorn, chocolate pieces, and peanuts in a large bowl.
Melt butter in a large saucepan over medium heat; whisk in flour until smooth, 2 to 3 minutes. Add brown sugar and corn syrup; bring to a boil, stirring occasionally, until sugar is dissolved, about 1 minute. Stir peanut butter into sugar mixture until creamy, about 3 minutes; pour over cereal mixture and gently toss until coated.
Spread cereal mixture over prepared baking sheet and allow to cool, about 30 minutes. Once cooled, break mixture into chunks and store in an airtight container.