Authentication apps like Google Authenticator or Authy work without any data service of any kind. Most services provide backup codes you can print out and keep in your wallet or another safe spot in case you lose or destroy your device.

You can print two copies of your backup codes, keep one in your wallet and one at home. You don't have to worry too much about them getting stolen because they are useless without your password. You can also generate a new set of backup codes at any time, which invalidates the old ones.

2-factor authentication does not require the second factor every time. It typically only asks for the second factor if the device is unrecognized, or the usage pattern is unfamiliar.

So, your laptop that's logged into GMail will stay logged in when you're out of the country. Unless you explicitly log out, it will stay this way.

I enter maybe one two-factor auth code a week, if that.

So:

i) Prepare ahead and log into your services.

ii) Walk to the nearest window, get the code, and go back to your desk.

iii) Replace your phone - you keep your number - request the auth key again.

None of these are completely seamless of course, but the idea is that all of the above happen rarely enough, and are mitigable enough, that it's far better than the alternative: getting pwned.

There are also second factors in the form of mobile apps, which eliminate the need for SMS, so as long as you have data/WiFi you're set. There are also ones that don't need data at all (see: the Battle.net Authenticator, which is basically a RSA key on your phone), but require more substantial initial setup.

This advice isn't incorrect, but it isn't entirely accurate either.

The Google Authenticator mobile app doesn't require data, so that meets the OP's requirements perfectly (ie, no SMS or data).

Use that, print out the one-time use codes and keep them in your wallet.

All the 2-factor entry boxes I've seen make the "trust" optional. If you want to be asked every time, just uncheck the box.

As far as I know's Google's authenticator app works by using a PRNG being seeded with a unique code for your account that's transferred when you first setup the authenticator and the current time. The app certainly works without a network connection.

AS for theft, you have backup codes which you should store securely (in a Truecrypt file with multiple backups or something), which allow you to log into your account once per code.

Why not print them out and put them in your wallet, like Google suggests. It's probably safer.

my solution is to have them in an encrypted evernote note

With gmail, you get 10 one-time use codes, which you can keep on a small slip of paper. So if you need to register on someone else's computer, you can use one of the codes and cross it off. If you lose the codes but not your device, you can print out new ones.

With google's 2FA, you can print out codes ahead of time that can each be used once in place of the SMS'd code. Bring some of those with you, perhaps...

When you are activating 2-factor authentication it gives you around 10 codes that you need to write down or print, to a wallet or under your freezer ets. However in university when I sit to a computer everytime I have to open a new clean Windows session, it leads me to enter 2-factor 4-5 a day. Thus I don't use it.

In google's case, you can print out a set of auth codes for times when you don't have your phone.