In a very large mixing bowl, combine the crispy rice cereal, rolled oats, and salted peanuts. Set the bowl aside.
In a medium microwave-safe bowl, combine the white chocolate chips, creamy peanut butter, and unsalted butter. Microwave on high in 30-second intervals, stirring after each interval, until the mixture is completely melted and smooth.
Stir the vanilla extract into the melted chocolate and peanut butter mixture until fully incorporated.
Pour the warm chocolate mixture over the dry ingredients in the large bowl. Use a large spatula to gently fold everything together until all the cereal, oats, and peanuts are evenly coated in the chocolate mixture.
Place the powdered sugar in a large, clean paper bag or a sealed plastic container. Add the coated cereal mixture in batches, close the bag or container, and shake vigorously until the pieces are thoroughly coated in a layer of powdered sugar.
Spread the finished reindeer chow in a single layer on a baking sheet lined with parchment paper and let it set completely at room temperature for about 30 minutes before serving or storing.