From Into the Wild, what are "rubber tramps" and "leather tramps?"
Rubber and Leather Tramps are descriptions that vagabonds use to describe a person's method of transportation. A rubber tramp has a car or other wheeled vehicle, and travels on the rubber tires. A leather tramp has no vehicle, and travels on foot, shoes often being made of leather. The distinction comes from both ease of travel -- a rubber tramp is more able to decide destination than one who relies on hitchhiking -- and an unofficial status: rubber tramps are sometimes seen as "less valid" than leather tramps because their vehicle is viewed as a luxury item. Chris started out as a rubber tramp in his old Datsun car, but soon found the opportunity to change his status:
With the battery dead there was no way to get the Datsun running. [...] Instead of feeling distraught over this turn of events, moreover, McCandless was exhilarated: He saw the flash flood as an opportunity to shed unnecessary baggage.
(Krakauer, Into the Wild, amazon.com)
As Chris had specific ideals about his vagabonding, he turned the abandonment of his car into a life event; he buried some of his possessions to recollect later and burned his money, throwing off the shackles of monetary and material goods to travel alone. In a way, the transformation of Chris from rubber to leather tramp acted as a turning point for him, allowing him to more fully realize his dreams of wandering the country without ties to society.
The "tramp" is a figure in the American mythos of the open road. A tramp lives a nomadic existence, having no fixed abode. Although the term is to a degree synonymous with "vagabond" or "vagrant," its connotations in popular culture are often romantic rather than derogatory. Often the life of the tramp is portrayed as countercultural, representing freedom and creativity.
Rubber tramps are those who own vehicles, either cars or motorcycles, and leather tramps are those who walk or hitchhike. Two iconic and romantic portrayals of "rubber tramps" as countercultural heroes are Kerouac's novel On the Road and the film Easy Rider.
In Into the Wild, Chris McCandless is an upper middle class young man who searches for an authentic life by becoming a tramp. He starts as a "rubber tramp" who owns a car but decides that the existence of a "leather tramp" is more authentic, and eventually travels to the Alaskan wilderness where he tries to survive completely on his own, without relying on civilized society at all, and dies.