tructions
Arrange 2 racks to divide the oven into thirds and heat the oven to 250°F. Line 2 rimmed baking sheets with parchment paper.
Place 8 tablespoons unsalted butter in a small, microwave-safe bowl. Microwave in 10-second intervals, stirring between each, until fully melted, 50 to 60 seconds total. (Alternatively, melt in a small saucepan on the stovetop over low heat.)
Place 4 1/2 cups Rice Chex, 4 1/2 cups Wheat Chex, 2 cups pretzel twists, 2 cups cheese crackers, 1 cup oyster crackers, and 1 packet of the ranch dressing seasoning mix in a large bowl, and lightly toss to combine.
Pour half of the butter over the cereal mixture and gently toss to coat. Sprinkle in the remaining ranch packet and butter, then gently toss again so all the pieces are evenly coated.
Divide the mixture between the prepared baking sheets and spread into an even layer. Bake, stirring every 15 minutes, until lightly browned and crisp, 45 to 50 minutes total. Let cool for 10 minutes on the baking sheets before serving.