Found it!

A talk.bizarre posting about fast food which I'm always (mis-)quoting.

If you don't have any ham, you can't make any of the sandwiches on the menu that mention ham in the ingredients list. Not even if you've already started. You can't make more ham. It arrives on the truck. If the truck isn't coming until tomorrow morning, you won't have any ham until tomorrow morning.

I was reminded of it by Jon's descent into delivery hell yesterday.