It used to be that if you got to the airport early, you'd head up to the official U.S. Post Office in the main terminal to pay your bills (on the theory that the best flight insurance is making sure your survivors won't find any embarrassing past-due notices), then do some banking, enjoy a couple of brews and take a look at the latest exhibit on the walkway heading toward Concourse A. But that was then, this is now. And in the post-9/11 world, no one dawdles on the way to security -- not because getting felt up by DIA's enthusiastic friskers is such a treat, but because you can't risk getting stuck in a slow-moving line. Which means, of course, that when you get through security quickly, your entertainment options are limited to the concourses. That's when it's time to head to Que Bueno! on Concourse B, where the burritos are so tasty, so big and so fat that it might take you a couple of hours to digest one. But fair warning: Que Bueno! is a lot more crowded than it used to be, which means you could waste many, many minutes waiting to order -- and then still more arguing that, yes, you really want that sauce fuego.