Technically, the FAA allows a third bag if it's camera gear. I've had to point that out to several non-TSA ID checkers in the past, as well as a few TSA agents (one guy I actually argued with for a few minutes; he walked up to me and said, "Someone needs to talk to you about carry-ons," to start a conversation, apparently; he refused to believe the FAA has rules allowing exemptions for camera gear, but as I wasn't even at the checkpoint yet, I walked away from the argument).

And I've had to point it out to one ramp agent for UA who felt it necessary, when I gate-checked my rollaboard for a EMB-120 flight, to tell me I had more bags than I was allowed (the "extra" was a very small--purse-sized, in fact--camera bag with two small lenses in it, on that particular flight, in addition to my laptop bag + 18" rollaboard).

But I carry a printout from the FAA site and one from the TSA indicating the exemption, and have never had to show it (yet).