Heat oven to 350°F. Spray cookie sheet with cooking spray. In large bowl, mix popcorn and cereal; set aside.
Empty jar of marshmallow creme into medium microwavable bowl. Microwave uncovered on High about 2 minutes, stirring after 1 minute, until melted. Stir. Pour over popcorn mixture, stirring until evenly coated. Spread mixture on cookie sheet.
Bake about 10 minutes, stirring after 5 minutes, until marshmallow coating is light golden brown. Spread on waxed paper to cool, about 15 minutes. Store in tightly covered container up to 2 weeks.