The audio cassette and VHS are long gone... childhood memories, that are no longer in use. In this day and age, it's all about the DVD or Blu Ray, and no doubt, that will change in the next decade too.
When I think about travel, I always make sure I have a portable DVD player in reach. A flight or train journey is much shorter when entertainment is at hand. Sometimes and MP3 just won't cut it, and the opportunity to pick up a DVD to watch right before the flight is always there.
Portable DVD players come in all shapes and sizes now. No longer are they bulky or dependent on recharging every hour. You can easily enjoy a domestic US flight, or travel between European destinations without worrying that your charge will run out. I for one will never leave my house without my player - and the evolving world of technology will only mean I will need a new device soon!