You can also use a small cat carrier type of thing or small gym bag. I use a thick layer of newspaper with some shredded newspaper on for absorption in case of a bathroom accident. Then it can be tossed out when you reach your destination and replaced using fresh newspaper that you could have with you.
Or you could use a plastic container as the other poster mentioned, good idea to have one with a locking lid, or use any suitable cardboard box. You could add a few airholes but they are not really needed as these are not airtight and beardie will not run out of air, just like we don't run out of air on a long drive in the car with no vent or windows open. Or think of being in a small room like a bathroom with no windows open. Even if you sealed all the cracks under the door you could still breath for days.