Back in the '70's I was way into Dave Van Ronk and even got a big J-50R Guild like the one he played. Later on I heard a couple of songs that I'd learned off his recordings featured in contemporary films. Fare Thee Well (Dink's Song) was collected by John Lomax in 1904 (Wikipedia says 1909, corrections welcomed here), Second Hand Songs called it a 'Folk song that tells the story of a woman deserted by her lover when she needs him the most. In 1904, ethnomusicologist John Lomax recorded it with his huge Edison recording machine as sung by an African American woman called 'Dink' in a tent camp of migratory levee-builders in Texas. It was published in 1934 in John and Alan Lomax's "American Ballads and Folk Songs". The Lomax recording is believed to be lost (or worn out at least).'
It was prominently featured in the Coen brother's film Inside Llewyn Davis, which was based on Van Ronk's posthumous memoir, The Mayor of MacDougal Street. Here is the film's star, Oscar Issac singing it with Marcus Mumford and some of the Punch Brothers providing the instrumental backing, Fare Thee Well (Dink's Song)

The other song was He Was a Friend of Mine. Willie Nelson sang it in the film Brokeback Mountain but I'm partial to the way Jerry Jeff Walker performed it on his Scamp CD. He Was a Friend of Mine