PREP: Line a large sheet pan with parchment paper and set aside.
COMBINE: In a very large bowl combine the Chex, pretzels, Cap'n Crunch, cheerios, and M&M's together.
MELT WHITE CHOCOLATE: In a medium-sized bowl add the white chocolate chips and vegetable oil. Microwave for 30 seconds, stir, and microwave for another 25 seconds. Stir until melted and smooth. If needed, return to the microwave for a little longer. (Bursts of 10 seconds stirring for 10 seconds in between each burst).
MIX SNACK MIX: Pour the melted white chocolate over the snack mix, using a spatula to scrape all the melted chocolate into the mix. Working quickly, gently stir until cereal mix is well coated in the white chocolate and then transfer to the prepared baking sheet and spread into one even layer.
LETHARDEN: Allow to harden at room temperature or place in the fridge until firm, about 10-20 minutes. Break into pieces and serve!
STORAGE: Store in an airtight container at room temperature for up to a week. We like this snack mix best within 3-4 days.You can freeze any leftovers in an airtight container/bag for up to 3 months; thaw at room temperature.
Nutritional information is for approximately 1/2 cup servings.