It seems like everything has an expiry date these days... I get the feeling that they are 1 part safety, 2 parts lawsuit buffers and 4 parts marketing..( if you throw it away, you go right back and buy more). I have to wonder how much the margin is on many of the products we consume as well as those we stockpile. Does bottled water really expire in so short a time if the plastic containers are not exposed to light? When one stores more food than one small family can reasonably consume while cycling those dates loom.
A good question! I guess it depends on a few factors, the nature of the foodstuff, the method of preservation, the container and the storage conditions. Personally I find that dairy products like milk and cream and some meat products especially chicken is generally right on the suggested date. Sometimes they can go off before that BBD and it is not due to the way I am storing them. Canned food is another story. I have consumed can food well beyond( a number a years) past the BBD. It tasted fine and I lived to tell the story but my wife thinks I'm crazy. I am not suggesting ANYONE do this, just relaying a personal experience. Again it will depend on the produce. Acid food sources like tomatoes tend to eat through tin cans after a few years are not edible. Also I would be wary of the plastic lined cans as the plastic can contain Bisphenol-A (BPA) which will migrate to food in time.
To me water is water. In properly sealed container, even plastic as long as it does not contain BPA, stored in a dark place, it should remain consumable for a very considerable time. In a SHTF situation where food and water become a premium I think that in most cases if you are prudent BBD will mean little and be the last of your worries.
Again these are my personal opinions. Keep in mind that about 5,000 people die in the US every year from food poisoning most caused by inadequate cooking and unhygienic preparation. Still it is a sobering thought.
Two of the best reads I could find on this topic. I do eat foods past the best before dates stamped on the cans and such. Typically I like to examine what I am eating, smell, colour and texture and cook a tad longer then normal. If it smells or tastes bad, it probably is and no amount of cooking can save it. but I have not encountered to many canned foods with weird smells or tastes. There was a good research study done on the nutrient levels in canned foods over an excessive amount of time, and found that levels remain in a good amounts even 10 to 15 years. best before dates are not expiry dates! they are simply ideal look and texture dates and have little to nothing to do with the foods safety level past that point.
http://www.ctvnews.ca/best-before-confusion-leading-to-needless-food-waste-1.744531 (for news article of the stamped dates and avoidable food waste)
http://www.stilltasty.com/ ( is an awesome website with a lot of good info on foods and shelf-life past best before dates!)
Never underestimate the power of free! If someone has deemed something valueless, yet U see value in it; Then you've already made a profit and savings!
My expiry date was 2010, I'm just too old to go stale. 
"We 'Prep.' to live after a downfall, Not just to survive."
Marketing? Big pharma wouldn't do that would they?
http://articles.mercola.com/sites/articles/archive/2000/04/02/drug-expiration-part-one.aspx
Than= I’d rather be rich than poor.
Then= I first became hungry then I ate.
There = She is there now.
Their = They have their things.
They're = They're going to the mall.
To = They came to the house.
Too = That's too bad.
