there should be a date on the box the packets come in, but I have this month cooked hot cocoa that went out of date a year ago. It tasted just fine, even better than the fresh cocoa.
But a cheaper alternative would be to make your own mix and seal it up in vacuum jars. Hillbilly housewife has all sorts of mix recipes that are cheaper than buying the premade ones. Here is the direct link to the mix page. http://www.hillbillyhousewife.com/homemadeconveniencefoods.htm they also have other mixes, like pancake mix, rice mix, etc.