You know, the leftovers that seem to multiply in your fridge, or the teeny, tiny bit of something you add that overwhelms what you add it to. For me, it’s when I’m out of chocolate ice cream and make due by sprinkling cocoa over vanilla ice cream. No matter how tiny the amount of cocoa I sprinkle on, I seem to end up with huge amounts of leftover cocoa powder in the bottom of the bowl.
Whenever I boil pasta, no matter how carefully I measure, I always seem to end up with at least half a serving more than I intended to make. I think my rotini are fertile and the hot water activates their breeding cycle. Either they have a very short gestation period, or they practices meiosis. Either way, they’re delish!
Heh… My sister had a container of baby powder that NEVER seemed to run out. It was down to that “shaky” sound that is supposed to indicate nearing empty status. But when you used it, you still got plenty of powder. It was too funny. I’m sure it’s run out by now though…(oooWEEEEooooo). 
sometimes the A-1 Sauce seems to last longer than it should…
coco powder on ice cream? dude, you can get choclate syrup SO CHeap! what are you thinking? are you into grainy?
No, but the cocoa powder is there. 
Urrgh! Moderators, would you please correct the title pselling? (I need new glasses).
Tortilla shells. My (ex) wife and I made tacos one night, as I went to the fridge to grab the tortilla shells, I found 12 old bags of shells and I think 5 bags of cheese. I made a new rule after that. Once the meat is gone a few days later, just throw out the remaining shells and cheese otherwise they make their way to the back of the fridge and get lost.
The Miracle of the Marshmallow Fluff.
Decades ago, I was chagrined to find my dream of a peanut-butter and marshmallow fluff sandwich crushed by a jar bereft of the stuff. Just a thin skin on the bottom of the jar, not even enough to bring any up on the tip of a butter knife.
Perhaps, I thought, if it were warmed, I might loosen that millimeter-thin skin enough to get just a taste. So the jar went into the microwave for a few seconds, after which I removed a practically full jar of marshmallow fluff. Joy!
One time at a New Orleans themed restaurant I ordered some kind of slushy drink, which came in a styrofoam cup that must have held a quart. I was sucking on that drink all night and the level never seemed to go down any, though my perceptions might have been affected somewhat by drinking a quart of booze-heavy crushed ice.
Somebody said once that eternity is two people and a five pound ham.