I'm really not comfortable unless I have a buffer of a few grand, no idea how people cope when running on empty!
Generally, they don't have a choice. You'd cope too, because you'd have to.
In the past, I've gone into the bank to withdraw the last couple of pounds of my overdraft so I could eat that day. It's how it is for some people, especially since our society is geared towards putting people into debt and keeping them there because it's more profitable.
Now I have a month's pay as a buffer. I did have 2 months's pay, but I decided to spend some on toys because I have spare money and I'll accumulate more spare money.
I am an anomaly, though, because I'm a boring and unsociable old fart who was lucky enough to be able to get a mortgage 20 years ago and who hardly ever goes anywhere past walking distance. Those things massively reduce my cost of living, so even though I'm a minimum wage flunkey I have spare money. I'm also on an old contract, so I can work 40 hours a week and get paid for those 40 hours. A rarity nowadays.
If I had to travel to work or pay average rent, I'd be living hand to mouth even on 40 hours a week. If I had what's now a normal contract, i.e. few or zero hours, I'd be unable to live without outside support. That's the norm nowadays because our society is badly flawed and hasn't adapted to changing times.
Saving even £100 simply isn't an option for a large and increasing proportion of people.