Earlier quoted context omitted.
I asked for "a doggy bag for this pizza please" and got the response "will foil do?" and it did just fine. We use foil to wrap stuff for the fridge quite regularly if it doesn't fit in a tupperware (reusable rubberised plastic food storage box). Of course if it's soup or whatever you're probably not going to get it to take away. Perhaps take your own tupperware with you, I'd love to see that. Sadly I so rarely get to…
Duh, you're right, any restaurant would have aluminium foil. I bet the question would surprise them though.
You: "can I have a mop bucket to take my food home in please?"
Waiter: "perhaps if we just wrapped it in foil ...?"