Airlines do in fact use excess cargo space to ship things for shipping companies / postal services. I’ve also heard before (I can’t verify though), that airlines are more than happy to leave your luggage behind if it means they can squeeze on one more piece of cargo since the cargo makes them much more money than they otherwise would have to pay you for delaying your luggage.
https://science.howstuffworks.com/transport/flight/modern/air-freight1.htm
Scenario 5: put it all in one big long docker-compose.yml and cross your fingers that docker isolation does its job.
E: definitely not what I do, no siree