Boxed cake mixes are convenient, of course: add a couple of eggs, oil, and water, slide the batter-filled tin into the oven, and you're done. But they can be versatile: Swap out that water for a liquid that'll add some oomph-coffee, for example, in a chocolate cake. Or use a bright, verdant olive oil in place of the neutral oil to add a layer of complexity to any boxed cake.