During our last trip, there was a fair amount of in-transit napping. On the second day of the trip, we were on the train, and I knew Elan was exhausted because he had skipped the nap the first day and been up in the night (too interested in what Mikhail and I were doing when we returned back to the hotel room at midnight after my friend's wedding). We brought the carseat onto the train, figuring he doesn't usually do well trying to sleep curled into a ball on a seat (hasn't napped on a plane since infancy). But there was a group of chatty 20-somethings sitting across from us, and you can't exactly ask strangers on a train to please stuff it so your toddler can fall asleep. He was doing his best to ignore them, but it wasn't quite working. So I came up with the (ahem, brilliant!) idea of letting him listen to music on the ipod. We found a suitably soothing tinkly music box rendition of U2 tunes, and he was out in less than 2 minutes.
Needless to say, we used this trick several more times for car trips. Unfortunately, now he thinks he can hijack the earphones while traveling on the plane too.