Almost every character in the MCU is in Avengers: Infinity War and that includes the Guardians of the Galaxy. Fans have been excited for years to see the Guardians meet the Avengers, but there are no questions that the two teams share a different tone. To better ensure that the Guardians were still on brand while meshing with the Avengers, James Gunn helped as an executive producer. While we previously knew that Gunn contributed some dialogue to the film, Gunn also had a hand with perhaps the most important aspect of the Guardians: music. As he recently revealed on Twitter, he was the one who picked "Rubberband Man" by The Spinners as the song to bring the cosmic adventurers into the action.
When working on Avengers: Infinity War, which stars several franchise leads melding together for the first time, directors Joe and Anthony Russo and writers Christopher Markus and Stephen McFeely made sure to collaborate with the other creatives of the MCU to make sure that everyone was in-character. This included James Gunn, whose Guardians of the Galaxy are very much tied to his own sensibilities. That extends to the importance of music in the Guardians of the Galaxy, which come from Gunn's personal tastes. It makes a lot of sense then that when it came to picking the song that introduces the Guardians in the movie, the Russos left it up to Gunn.
Knowing full well that he's going to be asked this question for a long time (even though he's answering it right now), Gunn took to Twitter to explain that he was the one who suggested the music the Guardians listen to in the blockbuster. Gunn offered the Russo's three different choices, but they ultimately picked the song that went in the movie. And yes, nerds, it came from the Zune that Peter Quill got at the end of Guardians of the Galaxy Vol. 2.
At this point, everyone knows just how important music is to the Guardians of the Galaxy franchise. Finding out what the soundtrack would be for Vol. 2 was almost more important than learning what the actual movie was about. James Gunn puts a lot of thought into what song he puts into what scene and why. It'd be pretty difficult for someone else to just come in and do the same thing. It's good to hear that Gunn pitched his own ideas, proving just what a collaborative process the making of Infinity War was.