How do you manage data between your primary and travel-phone?

I _think_ you would need a fresh iCloud account (thus losing access to purchased apps and subscriptions). You also need to manually create fresh social media accounts, copy over contacts, etc.?

Any advice on how to automate this process or is this just a 2-4 hours exercise you do before your trip?

A couple of hour exercise setting up the minimal amount necessary for the travel beforehand. Then once you're at destination, you can set up everything else if you want.

I don't have a lot of "everything else" anyway, so my device would probably look suspiciously 'clean' even if it was my in-this-moment daily driver. (HN is my news and social media). I don't use banking apps, but the irony is that I would need to whilst overseas.

One of the funny things is, I should be able to re-setup any device with an old gmail account at any time in any place, but with all the extra security these days, you need an old device to authorise the setup of a new device. I'm going away early next year, so I'll need to have a dry-run of the setup...

You mostly don't sync any such data. Prepare some file (or a few files, including an .ics for itinerary or what-not) with information about your trip, a few days in advance, and copy the file(s) to the phone. That's it.

And if you use iCloud or any of that stuff - you've already lost; Apple, and the US government already have access to your files and communications before you ever came to the airport. Sure, maybe it's not the specific border guards who have the access, but still.