Firstly, the Google Authenticator application does not require a network connection. See: http://support.google.com/a/bin/answer.py?hl=en&answer=1...

If you are planning to be without your phone, you can always disable 2-step verification temporarily: https://support.google.com/accounts/bin/answer.py?hl=en&...

Finally, if you lose your phone, you should always have your single-use backup verification codes to allow you to login.