Start with the cake. Regular boxed white cake - follow the directions on the box, but lessen the water by 1/3 of a cup and add in Strawberry preservatives (about 1/2 the jar - depending on how strawberry you want the cake).
Once cake is baked and cooled, I covered the top in Coolwhip and made the flag out of blueberries and halved strawberries! Delicious and healthy... enjoy. :)