When I moved in, I slung four full ammo cans into the corner of a closet. I have since pulled out Can #1 (which contained a variety of premium +P and +P+ .38 Special JHP) and Can #2 (.45ACP ball) and taken them to the range.
I know Can #3 is full of 55-grain 5.56mm FMJ from Georgia Arms.
I have no recollection at all what is in Can #4.
I almost don't want to open it. As long as I don't, it could be full of anything: precious .44-40 or .32-20, 9mm I badly need to feed the Para LTC 9, a zillion rounds of .22LR to keep me plinking for months... I'm sure when I open it it's going to turn out to be corrosive Romanian 8mm Mauser or 12ga birdshot or some 7.62x39mm left over from when I had guns chambered for 7.62x39.
But as long as I don't look inside, it's Schrödinger's Can and I can imagine it full of whatever I want.
UPDATE: I was weak. I had to look in the can. Highlight below for spoiler...
The downside? It wasn't full of precious, precious .44-40 or .22 Remington Jet. Upside? If I need to fend off the zombies with my Steyr-Mannlicher stützen, I am squared away with 8x56mmR already loaded on en bloc clips.