This is the series' 300th episode.
When the boys walk into the liquor store at the beginning of the episode, behind them on the wall is a lit sign that says FB beer company. Jensen Ackles started The Family Business Beer Company brewery in 2017.
One of the items in the pawn shop inventory book is Unicorn Urine
Zachariah refers to Castiel as Constantine. The character of Castiel was modeled after the character John Constantine from DC Comics, complete with trenchcoat, tie, and white Oxford shirt. Constantine briefly had a TV show on NBC: Constantine (2014). After the show was canceled, the character of Constantine was incorporated into the TV show Arrow and later DC's Legends of Tomorrow, which was broadcast on the CW network, the same network as Supernatural.
At the pawn shop, in the back room, there was a hockey mask belonging to Jason of Friday the 13th (1980) fame. Incidentally, Jared Padalecki did star in the Jason-centered reboot of the horror film Friday the 13th (2009).