Heat oven to 300°F. Spray large roasting pan with cooking spray, or grease with shortening. In large bowl, mix cereals, pretzels and walnuts; set aside.
In medium bowl, beat egg white, orange juice, sugar and cinnamon with wire whisk until well blended. Pour over cereal mixture, stirring until evenly coated. Stir in popcorn. Spread in pan.
Bake 25 to 30 minutes, stirring every 10 minutes, until light brown and crisp. Remove from oven; stir in apple chips. Cool completely, about 10 minutes.