Heat oven to 350°F (325°F for dark or nonstick pans). Grease bottoms only of 3 (8- or 9-inch) round cake pans. Make cake batter as directed on box. Divide batter evenly among pans (about 1 2/3 cups batter in each).
Bake 18 to 22 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans to cooling rack. Cool completely, about 30 minutes.
Spoon 1 container frosting into large bowl. Coarsely crush 3 cups of the cereal. Add crushed cereal to frosting; mix well. Spread half over first cake layer to within 1/2 inch of edge. Place second cake layer over frosting; top with remaining frosting. Top with third cake layer.
Frost side and top of cake with remaining 1 1/2 containers frosting. Sprinkle with remaining 1/2 cup uncrushed cereal.