Preheat your oven to 250°F (120°C). Line a large baking sheet or two with parchment paper.
In a large mixing bowl, combine the Rice Chex, Corn Chex, Wheat Chex, pretzels, mixed nuts, holiday M&M's, and popcorn. Mix well to ensure even distribution.
In a separate bowl, whisk together the melted butter, Worcestershire sauce, garlic powder, onion powder, smoked paprika, cayenne pepper (if using), and a pinch of salt.
Pour the butter mixture over the dry ingredients. Gently fold the mixture with a spatula until everything is lightly coated.
Spread the Chex mix evenly onto the prepared baking sheet(s). Bake in the preheated oven for about 1 hour, stirring every 15 minutes to ensure even toasting.
Once done, remove from the oven and let it cool completely on the baking sheet. The mix will crisp up as it cools.
Once completely cool, transfer the Chex mix to an airtight container for storage or serve it in a festive bowl for snacking.
Notes
For a festive touch, serve in a holiday-themed bowl or small gift bags.