If you want to be different and make your own version, you can add flavors like blueberry, raspberry, or whatever the recipe calls for.
Or, just use whatever ingredients you have at hand in a pinch - but keep in mind that your mixture will not rise nearly as much as commercially prepared brownies do.
The cookies will still be quite dense and taste good, but there's no way to add more sugar.
There is one thing you must remember if you go with a homemade recipe - the most important factor in how good the brownie is will be the texture of the cookie dough.
This means no flour, sugar, or baking powder - just the right kind of cookie dough.