I have actual, firsthand experience of being the next customer in line, not once but twice. 2 different McDonald’s, both in Urbana-Champaign.
In each case, the person behind the register didn’t seem surprised, but calmly told the person doing the ordering that their cash registers had a $99.99 limit (almost certainly untrue, but they were talking to an inebriated frat member who was low enough on the totem pole to get stuck going out for them) and that after $99.99, they’d have to go to the back of the line to order more.
Depends on the place. There’s a Wendy’s in a truck stop in Carlisle, PA (on 11 just before the PA Turnpike) which has the fastest staff I’ve ever seen. They do get a lot of long-distance bus traffic. I’ve seen a couple instances of the driver letting everybody off the bus for food, then going to shower, and by the time he was done, everybody from the bus had received their order and was chowing down.
In the ‘old days’, a sign saying “Buses Welcome” was a pretty good indicator of speed-of-service.