I was going to get a Passport card but I figured why bother if I can get back in using existing documentation. What do I need to bring?

Here is a link that should answer all of your questions.

http://travel.state.gov/content/passports/english/passports.html

Click on the "Do I need a passport" tab.

Your link doesn't work.

I'm mainly interested in people who have already gone to see if they were able to get back without a passport card or passport.

Here is a link that should answer all of your questions.

http://travel.state.gov/content/passports/english/passports.html

Click on the "Do I need a passport" tab.

I had a surgery buddy who was in my group (via A Lighter Me in Tijuana) who did not bring her passport with her due to a delay with processing her application. She brought a letter from the US Passport agency stating it would be delayed (I don't know the reason as to why it was delayed though), her birth certificate and social security card. I know she made it back home.

However, I would suggest that if you have time to get your card, do that. It will make your re-entry back into the US a lot quicker! My re-entry took all of 3 minutes.

Cheers!