I was on a convoy, between Larnaca and Nicosia, on the island of Cyprus. It was hot, and I'm talking middle east hot.
Our vehicle, a wheeled lightly-armoured personnel carrier, decided to pack it in halfway to Nicosia, and there we were: Skinny Bill, my co-driver, and Tommi Potx stuck on the side of the road with what we had in our pockets: some Greek Cypriot pounds, Turk Cypriot lira, smokes, a lighter, a compass, dogtags, and a wallet with a totally superfluous U.N. ID card.
So, ever since that long, hot, thirsty afternoon, when on just about any task, I've carried a small pack or belt kit of some kind, with the items needed to see me through 24-48 hours, until the vehicle is recovered, or we exfiltrated. Even now, after getting out of the army after 25 years of service, I find the Battle Belt (Belt Kit aka Man Purse or 'Murse') indispensable when camping, hiking or cycling, or when the apocalypse arrives...
Step 1: The Belt Kit Complete
The key to almost all systems today is 'modularity'. Pieces are added or removed according to what you're up to. You'll end up with a belt kit that will get you throigh WWIII or the Zombie Apocalypse.