I like to buy cake mix when it's on sale, but then I often lose track of how long it's been sitting around. So when I bring it home, I've learned to stash it in the freezer right away. Saves wondering whether it's fresh when I get around to using it.

In your case, rather than risking a flat cake, I'd just make cookies out of the mix. The basic recipe, in case you don't know it, is:

1 (2-layer) cake mix
2 eggs
1/2 cup of cooking oil

Mix together by hand to a stiff dough, drop in rounded teaspoonfuls onto an ungreased sheet, and bake at 350-degrees for 7-10 minutes.

It's a cinch!
For variety, stir in extra ingredients, like chips and/or nuts, that are compatible with the flavor of cake mix. My particular favorite is toasted pecans with butter pecan or caramel cake mix. Cherry cake mix is good with white chocolate chips and shaved almonds. Let your imagination go!