Food in the Freezer:
If you can't tell the difference between your ice cubes and your ice cream, it's time to throw BOTH out.
Frozen foods that have become an integral part of the defrosting problem in your freezer compartment will probably be spoiled (or wrecked) by the time you pry them out with a kitchen knife.
Food in Fridge:
When something starts pecking its way out of the shell, the egg is probably past its prime.
Milk is spoiled when it starts to look like yogurt.
Yogurt is spoiled when it starts to look like cottage cheese.
Cottage cheese is spoiled when it starts to look like regular cheese.
Regular cheese is nothing but spoiled milk anyway...if you can dig down and still find something non-green, bon appetite!
If opening the refrigerator door causes stray animals from several block radius to congregate outside your house, toss the meat.
For other items, you know it is well beyond prime when you're tempted to discard the Tupperware along with the food.
Anything that makes you gag is spoiled (except for leftovers from what you cooked for yourself last night).
Food in the Pantry:
Any canned goods that have become the size or shape of a softball, should be disposed of very carefully.
Fresh potatoes do not have roots, branches, or dense, leafy undergrowth.
Sesame seeds and Poppy seeds are the only officially acceptable "spots" that should be seen on the surface of any loaf of bread. Fuzzy and hairy looking white or green growth areas are good indications that your bread has turned into a pharmaceutical laboratory experiment. You may wish to discard it at this time, depending on your interest in pharmaceuticals.
It is generally a good rule of thumb that cereal should be discarded when it is two years or longer beyond the expiration date, or when it will no longer fall out of the box by itself.
Flour is spoiled when it wiggles, or things fly out when you open it.
Raisins should not usually be harder than your teeth.
Salt never spoils. However, if you can't chip off reasonable amounts from the block, maybe another box is in order, as fresh salt usually pours.
Most spices cannot die, they just fade away. They will be fine on your shelf, forever. (Put them in your will.)
If your grandmother made the vinegar, it is probably still good.
This is not a marketing ploy to encourage you to throw away perfectly good food so that you'll spend more on groceries. Even dry foods, older than you are, need replacing. Perhaps you'd benefit by having a calendar in your kitchen.