www.cakemixdoctor.com is a website with a forum that has wonderful ideas cookies and bars of course done with cake mixes.
The one I use often is devils food chocolate cake mix with 2 eggs and 1/4 cup oil I think? and make cookies out of it. But since my family goes crazy when peanut butter is in anything, I tend to put peanut butter chips on the top of the cookie right before it is baked!