Preheat the oven to 300 degrees F. Line 2 large rimmed baking sheets with parchment paper.
Stir together the cereal, cheese cracker chips, pretzels, peas, nut and ramen noodle pieces in a large bowl. Stir the reserved seasoning packet into the melted butter. Pour over the cereal mixture and toss to coat.
Spread the mixture between the prepared baking sheets and bake until golden brown, about 12 minutes. Cool completely before serving, about 10 minutes.