The book Sam finds that is concealing the button that unlocks Emily's room is titled, "How To Serve Man," - which references the 1950s short story, "To Serve Man." It tells about aliens who come to earth. At an UN session, the aliens tell the humans that they are there to provide them with peace and plenty. They supply them with cheap unlimited power, a device to suppress explosions, and drugs for prolonging life. One of the characters steals a book from the aliens and translates the title to "To Serve Man." He believes it is a guide the aliens use to 'provide for' and 'take care of' man. After further translation, he discovers that it is actually a cook book. This story aligns very closely with the Leviathan's plan for man: They are secretly purifying the gene pool, curing cancer, and ending hunger in order to harvest their perfect food supply... all with the public image of "serving man for the greater good."
The fat man the Winchesters take blood from is wearing a Plucky Pennywhistle t-shirt from the clown themed restaurant chain that featured in Plucky Pennywhistle's Magical Menagerie (2012) and the bench has an advertisement for Biggerson's Restaurant.
In the town full of human happy meals Dean says, "It's freaking Woodstock. Everybody's hopped up on the brown acid". At the 1969 Woodstock festival someone got onto the speaker system to warn everyone to watch out for acid (LSD) dispensed on brown blotter paper. Supposedly this particular batch of acid was giving some users a very bad experience.
When Dick and his assistant are talking about replacing Gloria the news lady, the assistant asks what to do with the body, and Dick replies "Call chef Fieri, I feel like barbecue", likely a reference to Guy Fieri, a well known tv food critic.
When Sam and Dean head into the vampires' mansion, a painting can be glimpsed in the hallway just outside the dining room where the Alpha Vampire is waiting for them. The work is "Saint Michel terrassant le démon" by artist Josse Lieferinxe - one of many Michael vs. Lucifer depictions used throughout the Supernatural series. This particular one was previously seen in Lucifer Rising (2009) as part of the angels' "green room" where Dean was held captive.