I knew generally that food labels did not always mean expiration dates; but I did not quite know the extent to which this went... especially the differences between "sell by" and "best by" and "use by" dates. In terms of changing my habits, this one has been difficult, because I cannot rely on my senses as much as other people to tell if food is still safe to eat. My allergies and migraines do strange things to my sense of taste and smell (hard to do either when your nose is always blocked up and your head always hurts!), and obviously, some bacteria/mold isn't the most visible... but, to counter this, I've been paying special attention to changes in texture (which I almost always notice) and changes in color, which can tell a great deal. For example, I noticed that my grape juice was "off" when, after about 10 days of sipping on it and it tasting fine and being relatively sweet and mild, it sort of turned into this super-sour, ultra-dry juice with a grainy texture. While not necessarily a bad flavor (after all, I would assume that's how they make wine...) it definitely wasn't the sweet grape juice I once bought!