I do though in other words "I can have my own stuff in any car immediately, it's especially nice on holiday in a rental"

I used a car-sharing service (Communauto) for a while when I was between vehicles, and it was invaluable to just plug in my phone and not have to worry about setting up anything else. No menus to navigate, no signing into spotify or google maps or even pairing bluetooth. Just plug in, yes trust this car, go.