Combine Chex cereal, Cheerios, pretzels, and M&M’s in a large bowl.
Microwave white chocolate for 1 minute, then stir in 30-second intervals until smooth.
Pour melted chocolate over the dry ingredients and stir to coat evenly.
Lay the coated mix on parchment and let it cool for 15 minutes.
Once firm, break into chunks and store airtight.
