Is there a way to make a portable iOS backup?
I'm going to posit this as an answer.
Though I've never tested it 'in anger' it does work after a migration, so might work on a simple 'file copy'…

Your iTunes 'iDevice' backup is stored in ~/Library/Application Support/MobileSync/Backup
so in theory, carrying that to another Mac ought to allow a restore.

The untested part of my theory is whether or not the iCloud sign-in &amp; encryption factors are also contained within that structure. The sign-in, presumably will just ask you to confirm with your ID &amp; password, then check against Apple's servers, but the encryption [assuming you use it to preserve your passwords etc in the backup] is another factor.

All I could suggest would be to test before it becomes critical - if you have another computer to test with, or even on a new, 'blank' Mac account, before you go away.
If it failed at that point, you'd have your 'real' backup at hand.

As the saying goes, a backup strategy is only as good as your ability to restore it.