Let me hop into the way, way, way back machine for a couple of minutes:
Back in the late 90's, I was a manager at several McDonald's restaurants in the Boulder, CO area. I would have to put together several bank deposits in a day.
First, a tally would be made of all the cash and checks, and a deposit slip filled out.
Then the money and checks would be put into a bank specific plastic bag, that then gets sealed.
As a rule, when we would have a Shift Manager run a deposit to the bank, we always made sure that the bank deposit bag was placed into a food bag before the deposit was to leave the office area of the store. Also, once the deposit was placed in someone's hands, they were to go directly to the bank, and no longer assist anyone in the store with anything.
This way, if anyone was to see an employee leaving the counter area, they wouldn't know that the employee was carrying a bank deposit, and wouldn't be a target of a robbery.
The rule was that the deposit bag stayed in the food bag all the way until the employee was at the bank teller window. Not while in line. Not while in their car. Period. During my time there, no employee from my store was ever robbed.
So, I would need more info if the bag was full of loose cash, or if the couple tore open a plastic bank deposit bag in order to see how much cash was there.
If the bag had loose cash in it, I would immediately suspect that an employee in the drive through was skimming cash from the register, and someone accidentally sent it out as an order, which also doesn't make sense, because the order should be double checked before it's handed to the customer, anyway.
Glad I haven't worked for McD's in nearly 20 years, that's for sure.
BC.