Preheat the oven to 250°F.

To two large roasting pans or casserole dishes, add the Wheat Chex, Rice Chex, Cheerios, pretzel sticks, Cheez-It crackers, mixed nuts, and pecan halves. Stir to combine.

To a medium saucepan, add butter, Worcestershire sauce, salt, garlic powder, onion powder, and celery seeds. Place over medium heat, stirring occasionally, until melted.

Give the seasoned butter mixture a good stir, then pour it over the cereal mix. Toss or stir the cereal with the butter mixture to coat it as evenly as you can.

Transfer the baking dishes to the preheated oven and bake for 2 hours, stirring every 30 minutes.

Let this cereal mix cool completely before covering in airtight containers to store.