All you got for me is light beer? was a catchphrase from a series of television commercials in 1979 for Coors Light beer. In the commercial, a man who is thirsty after spending the day performing hard labor for a friend is disappointed at first when his friend only offers him a light (low calorie) beer, but is surprised to discover that Coors brand tastes better than other light beers.
The evening that Marty came home and found the family's car was wrecked, Biff Tannen attempted a joke as he helped himself to a beer from George McFly's refrigerator by saying, "I have your car towed all the way to your house, and all you got for me is light beer?"
Biff's use of the phrase is ironic for two reasons; first, having the car towed didn't require very much hard work on his part, and second, he rewards himself with a beer even though the accident was a result of his drinking beer while driving.
"COMMERCIAL Coors Light - Setting up fence posts (1979)" YouTube video, posted by kaiBiggins, Oct. 14, 2009.