Bryan Cranston was initially reluctant to accept the role of Sal, since his busy schedule had him juggling a TV series, multiple movies, a Broadway play, and a book tour. He was persuaded to take the part after being impressed by the story and the caliber of the cast.
The novel which inspired the movie is a sequel to The Last Detail, also written by Darryl Ponicsan, which was similarly adapted to film in 1973. The Last Flag Flying's director, Richard Linklater, has stated that the two films, however, are not connected.
In the novel, which is an actual sequel to The Last Detail, the renamed character played by Laurence Fishburne is a minister. And the actor who played the original character from the 1973 film The Last Detail, Otis Young, also became an ordained minister in his later years.
Cinematographer Shane Kelly filmed the movie using a Panasonic VeriCam. He worked with Richard Linklater to give bleaker and more somber tone compared to their previous collaborations with a darker hue and muted colors.
Both Steve Carell and Bryan Cranston starred in another road trip film, Little Miss Sunshine (2006), even though they didn't share any scenes together. Also, both Laurence Fishburne and Cicely Tyson starred in Hoodlum (1997).
The link to the Vietnam war of which the three main characters are veterans is more evident in the filmography of Lawrence Fishburne who played Tyrone 'Clean' Miller in Apocalypse Now (1979). The 'Disneyland' sequence told by those veterans is reminiscent of the Playmate visit in the Coppola movie.