Jack Daniel
dice-universe.blogspot.com
It's in the LBBs at least.
I don't have my copies here - but I'm pretty sure it's the standard way older editions handled supplies. That was the irony I was trying to point out.
Now did people use it? Not that I could really say. In 198X we mostly didn't give a damn about encumbrance.
Ah, you're right, it's in Men & Magic, it's just not explained beyond a brief parenthetical found right there on the equipment table entry.