Preheat the oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a large mixing bowl, combine the vanilla cake mix, eggs, water, and vegetable oil. Mix according to package instructions until smooth.

Pour the cake batter into the prepared baking pan and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Remove the cake from the oven and let it cool completely in the pan on a wire rack.

Once the cake is cool, spread the whipped cream frosting evenly over the top.

Arrange the sliced strawberries in a rectangle on the left side of the cake to form the stripes of the flag.

Place the blueberries in the top left corner to create the stars of the flag.

If desired, use red and blue food coloring to tint some of the frosting for added decoration.

Garnish with fresh mint leaves if desired, then slice and serve the cake.