Depends on what sort of food it is. If it's meat or dairy, I don't fuck around with expiration dates (of course I'm in a significantly different situation than most). Canned stuff tends to be more about the condition of the can. Swollen, dented, rusted: dumpster time. Frozen stuff is the same way. Does it smell like it's been frozen since the ice age? I served a friend up a can of Coke that'd been in my fridge for 5 years (with informed consent, of course) and she didn't have a problem with it; wasn't even flat.