Preheat your oven to 250°F (120°C).
In a large roasting pan or a 13x9-inch baking dish, combine the corn cereal, rice cereal, wheat cereal, mixed nuts, pretzels, and bagel chips.
In a small microwave-safe bowl, melt the butter completely.
Stir the Worcestershire sauce, seasoned salt, garlic powder, and onion powder into the melted butter until well blended.
Pour the seasoned butter mixture over the cereal mixture and toss gently until all pieces are evenly coated.
Bake for 1 hour, removing the pan from the oven every 15 minutes to stir the mixture thoroughly for even toasting.
Spread the mix onto paper towels or a flat surface to cool completely before serving or storing in an airtight container.