Ever since I received a copy of the cake doctor I have been experimenting with cake mixes. The results have been amazing and delicious. By just starting with a basic vanilla cake and adding extras, you can invent a variety of flavours and textures.
Add about 150gms of white melted cooking chocolate for a white choc mud type cake
Swap some of the liquid component with alcohol for a more adult cake
Swap some of the liquid for caramel top n fill
Use 125gms butter and rub through the cake mix till breadcrumb stage add some rolled oats and you have a crumble topping
Leave out the oats and roll into balls put on a baking tray and bake and you have biscuits
Add hazelnut spread
Add peanut butter spread
Swirl some chocolate or berry sauce through cake mix before cooking
You don't have to limit yourself to just vanilla either
Take a chocolate cake mix, add some orange zest and replace some of the liquid with orange juice for a jaffa flavour
Add some raspberries
You get the idea. Because cakes mixes are designed to be 'bomb proof' you will end up with a cake/or biscuits no matter what you do.