What would be your go-to barebones TTRPG in a crisis?

What's the most comprehensive RPG you can think of that would serve you well if you found yourself with very few or no basic supplies to run it with? No rules on hand, pure memory.

Let's say Category 1 is games that could be run with as little as a pair of d6s (can be found almost anywhere) and some paper.

Let's say Category 2 is literally nothing. No dice, no paper, zip.