Cars are stolen mainly for two reasons 1)vehicle in question has may shared parts 2)vehicle is desirable

Your GTR obviously is in category 2. In Canada auto theft is really bad cars get lifted like crazy and end up in Russia and Ukraine.

Yes it is. I do it all the time. No issues.

Road trip? Across America. Boston to L.A. Just wearing an Apple Watch?

Legally I can carry insurance and registration electronically on my phone (which I do, no paper in the car) but drivers license still requires the physical version.

Not a problem at all. No different than doing it with a phone. Never carry the card and never been a problem.

pretty cool

Why does it matter geographically where you are? I don't understand the concern.

In my state we can keep our drivers license electronically on our phone, I keep mine in my Apple wallet.

Same in California. All my credit cards are also on my phone, as well as insurance information

Every credit card I use is stored on my watch and phone wallets, and I could absolutely get by on pretty much any trip with only either one of them. My watch also has its own cellular service, but even if you were completely out of coverage you can still make contactless payments as normal without any data or cellular connection.

Makes total sense. Why do you need any registration info on your device or paper they already know via your license plate.

Watch is basically just a small phone you wear on your wrist, wouldn't worry me.

when equipped with cellular

What does cellular have to do with using it as a key? Nada. Nothing. Méiyǒu shé me

I have the carabiner key for my Rivian and I bring it with me all the time. It's just super convenient to hang off a belt loop and open the frunk or rear hatch without having to unlock my phone. I've gone out without it, but it's a nice to have.