The 'brief safe' is a disguised safe that no one would ever touch because they look like poop-stained underwear. Or, you could just put your money in the bank, but that's such a silly idea no one would ever do that.
Nothing like sitting next a guy pounding on a typewriter while you enjoy your coffee.
Waterproof Passport Holder: You are banking on the fact that you will be rescued, right? Make sure to keep your passport safe to make your travel life easier after you are picked up.
Life Straw: Oftentimes, mining disasters are due to underground flooding. Bring along your Life Straw to give you some safe drinking water after you run out of your water pouches. And pack a snorkel while you're at it.