a friend shared this with me several years ago, and we use it regularly. No one believes me when I tell them there are no eggs or oil added. We made it for a birthday party when two of the guests were allergic to eggs.
1 cake mix
1 can pumpkin puree
1/3 cup water
Mix, then bake as usual. That's it - we've made chocolate cake, spice cake, and I've done it with a yellow cake, although we prefer chocolate or spice. And of course, chocolate chips are wonderful when added to the cake batter :) We've made cupcakes, mini cupcakes, round cakes and sheet cakes - they all turn out well.