My mother raised me with the motto "When in doubt, throw it out!" I toss stuff after a day or two. Lunchmeat, maybe 5 days. Tomato products, one week MAX. And things don't get heated up more than once. If we have leftover spaghetti sauce, I'll only heat what we will eat a second time and keep the rest refrigerated. I won't heat it all and stick the "leftover leftovers" back in the fridge.