It's the famous "curry-hook" mate.
Pull the hook out and hang the poly-bag handles on it so your take-away doesn't slide about the footwell.
Genius.
Edit: because I'm Scottish when I had my N16 it was a "carry-out hook" but same principle.
How have people not known about these, let alone not been using them!
How have people not known about these, let alone not been using them!