Isn't it better to factory reset a phone before entering the US and then restore a backup?
Apple Pay cards and so forth, anything with 2FA codes, in Sweden we use "BankID" which is largely using a private key in secure storage and a pin to "sign" and "identify" people, you would be destroying those things in an unrecoverable way.
Also, restoring a phone takes a seriously long time (8-10hrs?) and some things might not restore. Music you might have saved for example.
Also, your restore process might be using the internet (which is also an issue), but if it's not: then you're bringing your backups with you most likely, so they're forfeit.
2FA is a pain to recover, but it shouldn't that _that_ long to restore a backup unless you don't have decent internet access. All of my important data and apps usually take maybe 2 hours to get back (including flashing the OS), 3 if you include 2FA recovery.
Local backups is kind of an interesting risk/reward situation. My phone usually spends most of its time downloading apps from Google Play when recovering, the data recovery itself is very quick. Just backing up the APKs (which do not contain anything interesting) would probably cut down my backup recovery time to less than half an hour. Of course, my pictures and music are all stored in self-hosted cloud services, if you care to keep a local copy then things will take longer.
1) We're talking about people who are most likely going to be using 4/5G and Hotel Wifi. The US anyway is far behind on bandwidth, I get symmetrical 1G for "free" in Sweden, last time I was in the US it was $60/mo for 60MBit.
2) Phones have as much as 1TiB of storage, even at the speed of storage that'll take a hot minute.
Getting the 2FA codes set up while not having access to those 2FA codes is going to be interesting.
It all depends on the security pyramid you have, and how much risk are you okay with. I store all my passwords in Dropbox .kdbx file, but I need these always in case of emergency, even from a different device. So I must not enable 2FA on Dropbox. The password to it (and the .kdbx file) lives only in my memory. I hope not to get hit in the head.
If you're trying to protect your data, probably better to set up a secondary, plaubile profile, and restore from backup after crossing the border. Or to take a burner phone and buy a completely new one inside the US after crossing.