According to the poll below, 31% out of 55 respondents keep at least $100 reserve cash at home, and 12% keep less than $100
I have 2 kids aged 25 and 27; they each have their own apartment. I’m seeing them next weekend and will give them each an envelope with $120 to keep at home in case of emergencies. I’d been thinking about it for a while, and the article linked by @Spiderman is a good reminder.
As to how much cash I typically carry, $10 or 20. If I know I’m going to a cash only restaurant, $150.