Yes, your boarding passes.

SOP, as explicitly noted on the page prior to completing online check-in.

Then, if I were you I would go to CO.com to reprint your boarding passes.

Sorry, just having a little fun as it was just way too tempting an opportunity to pass up. In all seriousness. As noted in my second answer, AA.com does explicitly note that once you check-in online you cannot return to aa.com and check-in again or reprint your boarding passes. You can, however, print the boarding passes again if they are still displayed on your computer. I always make sure my boarding passes print successfully before closing my browser window. AA.com also notes that if you were unable to print your boarding pass that you would need to see an agent at the airport.