I once took a factory tour of the Whetstone chocolate factory in St Augustine. The tour guide explained that chocolate has an indefinate shelf life. Often when we see chocolate that has what looks like a biege colored "frosting" covering over it, this is simply the seperation of the coco butter, but does no harm. So as long as the chocolate does not melt, and is not eaten by either man or beast, it should be able to be stored in any manner. As for brownie mix, that is such a melange of incredients, I think it would be best vacuum packed with an oxygen absorber in it.
Nemo ME Impune Lacessit
Manus sapiens potens est