I'd buy him one of these books, depending on the type of person he is (and if he wants to confront the things to come):
Through a mirror, darkly from Jostein Gaarder.
Chasing daylight, from Gene O'Kelley.
Both are intimate and revealing, the first one also being beautiful despite the sad subject.
If he, on the other hand, prefers to ignore his impending death as long as possible, then it'd be probably better to buy some light or funny books instead that distract him ...