What are cakes used for?

Because the leavening agent has expired, you can't use the mix for anything which needs to "rise." But, unless the cake mix is full of weevils, or contains oil (and smells "off"), I can't see any reason you can't use it as "flour" - say for a crust or a crumb topping. Mix with butter/oleomargarine as you would for any crumb topping/crust. Add a bit of fresh flavouring - e.g. vanilla, almond or lemon extract, cocoa powder, cinnamon, nutmeg, or whatever suits your needs. Most cake mixes have sweetening, but taste the crumbs and see if you want to add more.