OK OK I know it sounded like a dumb question
Depends where you park though and how much change you need - in central London it's a small fortune if you want to stay for an hour or two.
And I don't always carry that much change around in my pockets so got used to keeping a stack of one and two pound coins (or one and two euro coins since I moved to Germany) in the car and wondered if there was a convenient place as I don't want them rattling around in the door compartment etc.
Not a biggie, will probably get a small container and keep it in the glovebox.