I worry too much about having enough reading material for trips. I even installed a book reader (Mobipocket) and a few "emergency" books on my Blackberry for spare time tiny-screen reading (of course there's plenty of reading material on my notebook too).
But still there must be books, and one dilemma is the hardcover, as in a book I am reading at home right now, Moon Lander: How We Developed the Apollo Lunar Module by Tom Kelly. It's good so far and I want to keep reading, but hardcovers are so bulky for trips. I'll probably take it anyway, along with a couple of backup paperbacks. One of these will be Hemingway's A Farewell to Arms, which I may have read in high school or college but don't remember. I'm hoping that some of Hemingway's spareness in prose will rub off on me. Not likely, I know.