This is a common occurrence in our house, even before we started stock-piling. There are just some things we don't eat often (mayo for example) that I almost wish we could buy it in sample sizes.
Happy Money Saver just posted a really great article on Expired Foods and just how long past an expiration date things are still good. If you are stockpiling, this is a great reference list you'll definitely want to bookmark (and maybe even print a copy to keep with your stockpile).
Read the Post Here.