I think the term Running away money was in (probably) the Mail, it might have been Jilly Cooper, but I do remember lots of us picking up the phrase
My mum always had bits like you Debih, she had her own bank a/c as well as their joint one so I'm not sure why, except when I was really poor she was able to help me in little ways without anyone else knowing.
We (only since last year) have a joint a/c, but each have our own too.
We have joint little stashes of cash; he empties his pocket of change (not that he ever has a huge amount as he doesn't buy much!), and if my purse gets a lot I empty it.
That all goes in jars and eventually we change it up and has always got added to holiday spending money
The years when we didn't go away (most of them), we'd still have the boys for a week so would use it for days out
At the moment we're on a mission to save for another holiday, so when we can are both putting a tenner in a bag - it's adding up nicely