I carry a lot of books when I travel, both in dead-tree form and, now, on my iPhone (via the Kindle app). Many, however, I have been carrying for a long time, trying to find the right combination of trip length, destination, interest, etc., to get through — so far to no avail. I like to call these book "ballast". They are dead-weight that you carry around, mostly to make yourself feel safe.
So, what are your favorite ballast books, the ones you carry around endlessly trying to convince yourself to finish reading but never do?
Here are some random examples of mine: