1 (18.25 ounce) package yellow cake mix
1 (8 ounce) container frozen whipped topping, thawed
1 pint blueberries, rinsed and drained
2 pints fresh strawberries, rinsed and sliced
Prepare cake according to package directions and bake in a 9×13 inch pan. Cool completely.
Frost cake with whipped topping. Place blueberries in a square in the corner, and arrange sliced strawberries as stripes to make an American flag. Chill until serving.