Early in the movie Harper James (Tye Sheridan) is watching an old black and white movie whilst laying on the couch. You see a couple driving down the highway. That scene is from the movie Detour (1945) starring Tom Neal and Ann Savage.
This is the second film where Bel Powley co-stars with a cast member from HBO's "True Blood". In 'Diary of a Teenage Girl' she worked with Alexander Skarsgård, and in 'Detour' she works with Stephen Moyer.