Unless you buy cake mixes for one, you're probably going to have too much left over. Use this formula to make two cakes out of one two layer mix.
List of Ingredients
1-3/4 cups cake mix from two layer box
2/3 cup water
1/4 cup oil
1 egg
Recipe
Combine ingredients in an ungreased 8 or 9" square pan and beat with fork until well blended. Spread batter evenly in the pan when mixed. Bake at 350 degrees for 30-35 minutes or until toothpick inserted in center comes out clean.