In order to make the cake, you will need water, vegetable oil, and eggs or egg whites, but the amount of each ingredient will depend on the brand of cake mix you buy. Most brands of 15.25-ounce white cake mix will call for 1 ¼ cups water, ½ cup vegetable oil, and 4 egg whites, OR 1 ¼ cups water, ¼ cup vegetable oil, and 5 eggs whites.  Some brands will also give you the option to use whole eggs instead of just egg whites. It is up to you which you prefer to do. Be sure to check the back of your mix to know for sure how much of each ingredient you should use. If you forget and throw away the box, the above amounts are likely to work for most standard white cake mixes. Note that these amounts only apply to standard 15.25-ounce white cake mixes – gluten-free mixes or mixes of a different size will require different amounts.