The actor was dying of cancer and was on his way to Mexico for experimental treatment. This innocuous-looking camper, with which he would spend time in the desert when he wanted to live incognito for awhile, is what took him to his appointment [or at least to the airport].
Inside with him was Billy Graham, of all people. They spoke of life and death and, in particular, the Kingdom. As they parted, Graham gave McQueen his Bible. It was in the actor's hands when he died a few weeks later.