Tricky. I read quite a lot, and if I want to re-read something I don't wait for an emergency. So I'd probably hope to pick something I've not read yet, more or less at random. Generally when I go away I try to download a dozen or more novels to my phone - but that depends on being able to recharge the battery.

If I had to pick something it would probably be by Neal Stephenson, such as Snow Crash, The Diamond Age, or Cryptonomicon.