M&Ms as a snack are hard to beat- you get a boost of sugar, it's an agreeable flavor that doesn't fight with coffee, and is a small shot of nostalgia. Every base I've been to has M&Ms offered as a snack.
I don't know what the military folk do in the hotter climates, though- I've never dealt with that problem.
The reason for the ammo can and M&Ms has more to do with keeping mice away than portability...