Measure out cereal into a large mixing bowl; set aside.
In a large microwavable glass bowl, add the chocolate chips, peanut butter, and butter. Heat in the microwave for 1 minute, stop and stir, then heat about 30 seconds longer or until mixture can be stirred smooth.
Add vanilla to chocolate mixture and stir thoroughly to combine.
Pour chocolate mixture over cereal, stirring until evenly coated.
Pour the chocolate-coated cereal into the food storage bag.
Add powdered sugar to the bag, then seal the bag and shake until the cereal is well coated in powdered sugar.
Spread cereal mixture out in a thin layer onto waxed paper. Allow mixture to cool fully.
Once cool, add cereal mixture along with M&Ms to a large storage container or storage bag. Mix or shake to combine. Store in refrigerator for up to 2 weeks.