In a large bowl, mix together the cereal, pretzels, popped popcorn, and M&M's candy.
In a medium microwave safe bowl, combine both bags of white chocolate chips with the oil. Microwave in 30 second intervals, stirring i between, until chocolate is smooth.
Pour melted chocolate over the cereal mixture, stir to coat.
Pour the snack mix out onto wax paper lined baking sheets and allow to cool until hardened (10-20 minutes).
When snack mix is cool, break into pieces. Store in an airtight container.