Sure! The only time I throw away expired pantry items if it is over a year old, unless it was chips or something. It usually only has expiration date because it can alter the taste if it old. Brownie mix, I am sure takes more than a month to start tasting off.
My brother works at a grocery store and often companies tell the store that if the food is expired to just throw it out and they'll get a credit for it or something like that. Anyways- he brings us things like cereal ALL the time. Usually those dates are actually "sell by" dates and that you have quite awhile to use it. Milk is the same thing- even if the date is old, it's fine as long as it tastes/smells good.