and where exactly do you keep it....?

A few hundred, a few thousand, more?

I've been putting cash from old car sales and random things I've sold into an envelope over time, and it seems like I should probably break larger bills into smaller bills and manage the cash better. I can't see scraping off shavings from a Krugerrand for bread when things go sideways, but at that point the cash would be likely be useless anyway.