If you are flying domestically... even if the flight is less than an hour... take at least two forms of government-issued ID.
Case in point: I lost my drivers license during my trip to New York City. The only ID I had was a few credit cards, and some membership cards, none of which had a photo of me.
Now technically, you don't need a photo ID to fly in the US. Specifically, the TSA rules state:
"Passengers who do not or cannot present an acceptable ID will have to provide information to the Transportation Security Officer performing Travel Document Checking duties in order to verify their identity. Passengers who are cleared through this process may be subject to additional screening. Passengers whose identity cannot be verified by TSA may not be allowed to go through the checkpoint or onto an airplane."
It is helpful to know the above rule, and it is useful to cite it should a TSA agent attempt to deny you boarding simply because you do not have ID. That being said, everything is completely up to the discretion of the agent at that point. Despite the tacky uniform and weary expression, it is vitally important to remember that a TSA agent is not a mall cop. They are real federal agents. In this post-Patriot Act world, they can make your bad day become a very VERY bad day. Be polite, be contrite, and be sincere. Don't argue, don't threaten, and don't condescend.
For a long time I didn't know what this blog was supposed to be. Somewhere along the line it became what it is—sharing the little things that are making me happy. I hope those things make you happy. (And maybe it's time for a new photograph.)