The book Greenwood decides to bring as present to the girl is "Franny & Zooey" written by J.D. Salinger, who lived as a reclusive for most of his life, just like Greenwood does in the film.
When Greenwood goes to his computer to see what Ellie's surprise is, the open tabs on the browser include Vice news, Pitchfork, AllMusic, Paul Thomas Anderson and French visual artist Jean Jullien.