On an overbooked flight I was on a few years ago, the cabin crew asked for a volunteer to travel in the jumpseat. The first volunteer was rejected by the captain because he smelled of alcohol, so I got the chance. I was given a very comprehensive briefing relevant to the cockpit and jumpseat position, rather than the usual passenger cabin briefing, and , in particular, how to evacuate from the cockpit in the event of an emergency via a rope thrown out of the window if the worst came to the worst!