In small bowl, mix sugar and cinnamon; set aside. In large microwavable bowl, mix cereals and popcorn.
In 1-cup microwavable measuring cup, microwave butter uncovered on High about 40 seconds or until melted. Pour over cereal mixture, stirring until evenly coated.
Microwave uncovered on High 2 minutes, stirring after 1 minute. Sprinkle half of the sugar mixture evenly over cereal mixture; stir. Sprinkle with remaining sugar mixture; stir. Microwave 1 minute longer. Spread on waxed paper or paper towels to cool. Store in airtight container.