During a karaoke scene, Henry Zebrowski's character Wade sings "Anthem From the Already Defeated" by Rock Plaza Central. This song was also featured in the 2012 film "The Battery". Both films were written and directed by Jeremy Gardner, who has leading roles in both films. Most notably, Gardner's character Ben in "The Battery" has a very memorable scene in which he sings and dances, bottle of booze in one hand and pistol in the other, to the same song.
In the karaoke scene, Justin Benson (Shane) sings "House of the Rising Sun." This is an homage to the song being used in "Endless"; Benson directed and starred in it.
Hank is watching "The Strangers" one night while waiting for things to happen.