In small bowl, mix sugar and cinnamon; set aside.
In large microwavable bowl, mix cereals and popcorn.
In 1 c. microwavable measuring cup, microwave butter, uncovered, on High about 40 seconds or until melted. Pour over cereal mixture, stirring until even coated.
Microwave uncover on High 2 minutes, stirring after 1 minute.
Sprinkle half of the cinnamon-sugar mixture evenly over cereal mixture; stir.
Sprinkle with remaining cinnamon-sugar mixture; stir; microwave 1 minute longer.
Spread on waxed paper or paper towels to cool.
Store in airtight contained.
Note: The cinnamon-sugar mixture blends in more evenly when it's sprinkled on the cereal mixture a half at a time.