Preheat your oven to 250°F (120°C). This low temperature ensures the mixture bakes evenly without scorching.

In a medium-sized saucepan, melt the butter over low heat. Stir in the Worcestershire sauce, garlic salt, and celery salt. Let the mixture warm gently, whisking occasionally, until the butter is fully melted and the seasonings are evenly combined, about 3 to 5 minutes.

In a large mixing bowl, combine the mixed nuts, all varieties of cereals, and pretzel sticks. Pour the buttery seasoning blend over the dry mixture, ensuring even coverage. Gently toss the ingredients with a large spoon or spatula until everything is well-coated.

Transfer the seasoned mix to a large roasting pan, spreading it out in an even layer. Bake the mixture for approximately 2 hours, stirring gently every 15 minutes to prevent sticking and ensure even browning.

Once baked to a golden perfection, remove the pan from the oven and allow the mixture to cool at room temperature for about an hour. This cooling step ensures crispness.

Store the cooled snack mix in airtight containers to maintain freshness and crunch.