In a large bowl, mix cereals, pretzels, peanuts and M&M's.
Melt white chocolate in a microwave-safe cup in 20-second increments until completely melted. (I use a large glass measuring cup.)
Pour melted white chocolate over cereal mixture and mix until completely incorporated.
Spread mixture between two greased 9 x 13-inch baking dishes.
Refrigerate dishes for 15-20 minutes until chocolate is set.
Break up into pieces and serve.
Valentine White Chocolate Snack Mix can be stored in an airtight container for up to two weeks.