Google allows you to print a set of codes [1] that can be used to access your account if your device is lost. I printed a set and have them stored in a secure place at home. Some people keep them in their wallet/bag/similar.
Advanced Protection uses a stricter implementation than
Google has offered in the past: Only those physical
keys—along with a password—will unlock your account. If
you lose them, you can't use a printed out backup code
So, no printed backup codes for Advanced Protection users!
Yes I have those printed and stored securely, and also my landline set as a backup phone number, but that doesn't really help alleviate my concern of "what happens if I'm abroad and no longer have access to my phone".
I guess keeping the codes with my at all times would work, but doesn't seem like that great an option (paper is easy to lose and easy to destroy). Maybe I should memorize some of them?
[1] https://support.google.com/accounts/answer/1187538