Any cake mix, add only 1 can of diet 7-up . Stir well, pour into rectangle pan (10x12 etc.) and bake using directions on box.. It will not rise as much but tastes like a regular cake. Strawberry is very good with low fat cool whip served on top and fresh strawberries.
If making a dark cake such as chocolate, add 1 can of diet coke, or any dark colored drink. Follow same routine above.
For a pineapple cake, use one box of angel food cake mix and add l whole large can of crushed pineapple, juice and all. Bake as directed on the box. I have only used a rectangle pan, but a friend made this in a regular tube pan and only had to cook it a little longer than directed. Use any diet clear drink such as diet 7-up.