In large bowl, mix cereals, pretzels, peanut butter candies and peanuts; set aside.
In 1-quart microwavable bowl, microwave white chocolate and butter uncovered on High about 1 minute, stirring once, until melted and chocolate can be stirred smooth. Pour over cereal mixture, stirring until evenly coated.
In large resealable food-storage plastic bag, toss half of the cereal mixture with 1/4 cup of the powdered sugar until evenly coated. Spread on waxed paper to cool. Repeat with remaining cereal mixture and remaining 1/4 cup powdered sugar. Store tightly covered at room temperature.