What's the greatest extent (as in the most amount of time) to which you've eaten something past its expiration date with the food still being enjoyable?
I believe they have recovered honey from Egyptian tombs that was thousands of years old and still edible. From recollection the syrup is too viscous for bacteria to colonise.
Fun fact: If you collect mad honey (the term for honey contaminated by bees which have pollinated poisonous flowers), you can wait for the poison to expire.