WARNING: The following contains major spoilers for Gunpowder Milkshake, now available on Netflix.
Many of Gunpowder Milkshake's significant moments take place in a location simply called the Diner. On the outside, it looks like a standard 1950s-style diner, complete with neon signs, a jukebox, vinyl booths, cheerful waitresses and an archetypal color scheme. The most frequently shown menu item is, as the title references, a classic milkshake, but there is another menu item that's a fun wink to a cult film.
Like in many 1950s-style diners, the menu is displayed on lighted boards behind the front counter. There are some screens that list menu items, but others show photographs of pinup women and the highlighted dishes. At one point, Sam (Karen Gillan) stands in front of the board and over her right shoulder the sign advertises a "Fight Club Sandwich."
This suits the slightly-off nature of the Diner. As soon as characters enter, waitress Rose (Joanna Bobin) asks if she can lighten their load. This is a polite way of asking patrons to surrender their weapons, because most of the Diner's guests are members of the criminal underworld. In the beginning, a teenage Sam (Freya Allen) is a well known customer, as her mother (Lena Headey) is herself a killer, and Sam continues to frequent the Diner into adulthood thanks to work.
The Diner is meant to work similarly to the Continental Hotel in the John Wick films, as it's a neutral location. Killers and gangsters can meet there to negotiate or socialize, and it's presumably safe since Rose confiscates weapons. Despite this, multiple shootouts take place at the Diner. While this Diner is like John Wick's Continental, references to other films continue beyond it, in large and small ways.
Fight Club is a well-known and brutal film combining elements of action, dark comedy and more. It doesn't have a lot of direct parallels to Gunpowder Milkshake, with Gunpowder Milkshake focusing on deadly women fighting a corrupt system, while Fight Club is about a man fighting himself. It doesn't feel like Fight Club influenced Gunpowder Milkshake in the way some action films like John Wick and Kill Bill did. However, Fight Club has been influential on the darkly comedic action genre, and Gunpowder Milkshake does fit loosely into said genre.
There aren't any other visible references on the menu board, though it would have been amusing to see more. When Gunpowder Milkshake gets a sequel, perhaps the menu will be updated in this way, but as it stands, the Fight Club Sandwich is still an amusing detail, and there are plenty more references to other films to catch in Gunpowder Milkshake, now available to stream on Netflix.