I've had a jar of mayonnaise in my fridge that probably dates back to about 2004.

It's one of the many jars and bottles of condiments—including mustard, orange marmalade, and miso—that seem to keep forever. I rarely use mayonnaise because I don't like the flavor much. In fact, now that I've started mixing my tuna salad with black olive tapanade, I never touch the mayo at all.

Still, it looks fine and doesn't cause my fridge to smell bad, so I thought it was fine to keep the jar forever. Apparently, I'm wrong.

According to a feature at CBS News's website, my rarely-used jar of mayo should have been tossed out about two months after I bought it.

The feature also clued me in about other staples that are past their prime. Pasta sauce, for instance, has a shelf life of about five days. After that, you can expect mold to start growing, even if it's not visible to the naked eye.

I don't use jarred pasta sauce, but I've usually got a couple jars of salsa stashed on the shelves. I figure salsa might stay fresh for a little longer—but probably not for the month or two that it usually takes me to finish them off.

On the other hand, I'm too quick to toss out cheese and eggs, which can stay fresh for up to a month or so. I've always assumed that they needed to be used more quickly than that.

A while back, I wanted to find ways to keep produce fresh. But for other foods, I turned to the Food and Drug Administration's site. I found a chart that provides helpful guidelines for how long food will stay fresh—and safe—in my fridge and freezer.

Frozen salmon, for example, is only good for three months. I guess this means I need to toss out a bag of salmon fillets that I bought from Costco about six months back. The irony, of course, is that I bought all that fish in bulk to save money.

And so, add this to my list of lessons learned the hard way: Bargain shopping is great for the things in my closet, but it doesn't work too well for the stuff in my fridge.