The soldiers in the film wear a unit patch with a large "22" on it. This is a fictional unit. The actual 22nd Infantry Division was a "Phantom Division" that never actually existed. It was created in World War II to fool German intelligence. The patch created is different from the one in the film, though.
Director Oren Moverman had wanted to have a scene with Will and Tony singing a song but couldn't decide which song to sing, and settled on Home on the Range after hearing the song being played from an ice cream truck while scouting locations. This is then paid homage to after Will's first notification when he's sitting in Will's car and an ice cream truck passes by playing Home on the Range.
During the boating & fishing scene, Woody Harrellsen's character yells out "Charlie don't surf!" The line originated from the 1979 film Apocalypse Now, set during the Vietnam Conflict. It was spoken by Robert Duvall's character during the film's surfing scene.