HEAT oven to 350ºF. Remove 2 Tbsp. cereal; set aside. Place remaining cereal in large bowl. Stir in measure of water listed on cake mix package. Let stand 2 min. Add eggs and oil as directed on package; mix well.
POUR into greased 13x9-inch baking pan. Bake as directed on package; cool completely.
FROST cake with COOL WHIP. Sprinkle with reserved cereal just before serving.