PC's going to hit the road with hope in their hearts and purpose in their stride. Once I heard 
Ain't No Grave I knew I was going to have to play it. 
Wayfaring Stranger too, probably. In some version.
What else is good in american folk? Instrumental, a plus. My usual mood music consists of 
Hex: Or Printing in the Infernal Method and 
The Bees Made Honey in the Lion's Skull by Earth, and the soundtrack from Dead Man, now I'm looking to add a little more hope and community to that. You know, folk.