If you're worried about security and want to give your Google accounts some extra padding; that is, you want to have a backup email address associated with your account just in case, you can now do so. Google Groups Guide 2 has written in Google Groups about how it's done:
To add an email address to a Google Account, follow the link below and add an additional email to the account listed under "Google account". If you want to add an email to another Google Account, simply select "change account".
To do so, go to https://www.google.com/accounts/AddNonGmailAlternate.
Forum discussion continues at Google Groups.
