[JDW11235]

What on earth does “Stacking Magazines” mean? It gave me a chuckle because I’m boxing them for fuel. LOL.

[grobdriver]

"Magazines" are what some people erroneously (generally media types) call "clips" for magazine-fed weapons.
It's a term similar to "keep your powder dry" only updated to modern weaponry.

The last, desperate defense involves stacking all of your remaining full magazines for easy access while you wait for the enemy to come.
Figuratively speaking, of course... but then again, maybe not.