I am pretty picky, but also used to go to sea where such things become pretty important. Here is the thing, It really depends on how the expiration is worded (in the US anyway) and what the item is.
A "sell by" date is just that ... usually on dairy products and such. It is NOT a "use by date. The rule is that it should not be kept a week after opening, regardless of the date. Closer to that expiration date, though and you take chances, because who knows if stuff was handled properly. A "best if used by date" (mostly on dry goods) means that you might not get the flavor/color after that date, but it should not be harmful (though use common sense .. if its got mold.. toss it!!)
Milk -- no more than a week after opening OR the "sell by date" You CAN, in a pinch use it a bit later, but heat it to a low boil (this will change the flavor) and its best to use in baking, etc... not to drink.
Eggs -- can keep a month. BUT, stores are notorious for adding old eggs to new cartons. Also, if you leave it on the counter ... watch it. Check by cracking onto a plate. The clear part closest to the yolk should stick up a bit. If it spreads out all over the plate, either pitch it or use it just to bake (you know they are thoroughly cooked in cakes, etc.. ) (yolk color, though means nothing except what the chickens were fed) BUT, remember even a fully fresh egg can carry salmonella, so either cook or pastuerize your eggs before eating.
cheese -- any
hard cheese, cut off the mold and you are good to go. Any
soft cheese (cream cheese, etc.) .. don't keep more than a day or so after expiration & PITCH if there is anything like mold on it.
Most other dairy (yogurt, etc.) is OK a day or two past the "sell by" date
usually (use common sense .. if it tastes, smells bad .. pitch it!).
DRY GOODS ... such as you described, usually have "use by" or "best by" dates rather than true expiration dates. Use common sense. (taste, smell, etc. .. any mold? bugs?) but generally the spices may lose potency, things won't tast quite as good as they should, but it won't actually hurt you.
Canned goods ... of course the old, watch for dents and such. But, if it is an "expiration" or "use by" date, you probably want to just pitch the item. If it says "best if used by" or something similar ...you can push a bit. It might loose some color, taste and nutrients, but as long as you use sense, won't be truly harmful.
To answer --- I have eaten cereal that was several years old, at my grandmother's once. It tasted "differant", so I checked the box ... after I had eaten it.
