General policy at American fast-food (Burger King) and fast casual (Chipotle, Panera Bread) is that they won't even send your order to the kitchen until you have paid. You can watch the screens, your order does not appear until you have paid up. This does not create a debt, obviously. But I'm not telling you anything you don't already know.
Heck when I order on my phone app and prepay, some don't even start preparing until I show up and announce myself!
So what's up with drive-through? Some drive-throughs have two windows: pay at the first, collect food at the second. That's how they handle that. However, it costs money to run two windows. They certainly have the right to calculate out the various costs:
- of building and staffing two windows, vs
- the bad reputation of slowing the line by making people wait for their food to be made, vs
- making the food "on spec" and risk having to throw it out.
Keeping in mind that the latter is not that weird: what practically defines fast-food is that food is pre-made in a production line. Even at Wendy's the burgers are custom built, but the patties are pre-grilled.
Fast food is all about flow, especially at busy times. So it wouldn't surprise me one bit if for that business, the calculus favors the latter option.
I would say that does not create a debt, because "get the food after you pay" is the norm in fast food.
So if you roll up with only a $100 bill, I certainly think it is within their right to say "no sale". After all, you did not damage them; it's their choice to decline the money. Again it is their right to make a business decision whether they will lose more money risking accepting counterfeits or throwing out food.