Sometimes there's a debate at my house whether or not something is still good. It's probably a universal issue, and usually centers around produce, milk and my desire to use food before I deem it to be bad.
I have this drive to ensure that stuff gets eaten when we purchase it. And if there's any doubt in my mind, it gets tossed. My wife has the same rule. With an infant in the home, there's no room to take chances.
Some foodstuffs are easy to know how or where to store it, others may confuse you.
This article from the Orange County Register goes over some points when it comes to food expiration.
Milk is one that's debatable. According to the article, the date stamped on a carton of milk is voluntary. In my experience it's generally pretty accurate. I'll notice the smell change after the "use-by" date, but the taste hasn't caught up just yet.
I personally wouldn't take the chance much beyond the stamped date on a carton of milk, or other dairy products. Same goes for mayonnaise.
For produce, specifically potatoes, I'll look at the spud to see for any rotten areas, mold, etc. If it's small enough, then I'll cut it away and use the rest of the potato for mashing or frying potatoes.
The only part of the storage area I don't do is olive oil. Mine is kept out of the fridge, and has never (to this point) gone rancid or spoiled sitting on the counter next to the range. Not to say that it won't, but it hasn't happened to me.
Hopefully these helpful reminders will keep your kitchen in the safe zone when it comes to food.