Who were Jan and Bob Buress and how did they help Chris?

They were a drifter couple in a van:

McCandless turned right on U.S. Highway 101 and headed up the coast. Sixty miles south of the Oregon line, near the town of Orick, a pair of drifters in an old van pulled over to consult their map when they noticed a boy crouching in the bushes off the side of the road. “He was wearing long shorts and this really stupid hat,” says Jan Burres, a forty-one-year-old rubber tramp who was traveling around the West selling knick-knacks at flea markets and swap meets with her boyfriend, Bob.