Today is Boxing Day in the UK so there were lots of reductions on food. I bought a Yule log for a pound which is best before today, but it will last for a few days as I can't eat it all in one go. We bought a cauliflower for 32p that is best before today and that will last a few days in the fridge as well.
My father found an unopened packet of pancake mix from 2 years ago and made them and we ate them and we were fine, as it was only flour, slat and some bicarbonate of soda; so as long as you are sensible you will be fine. Think of the time when there were no sell by dates, people had to judge for themselves what was good and bad.
In addition, if a homeless person had the food, would they quibble over something that was a few days past it's sell by date? That or hunger? As long as there is no mold, I tend to think it's fine. Dates can be deceiving, after all a computer stamps it on, so it could be computer error as well. People sometimes mix the made dates with the sell by dates, as some products stamp when they were made too.