"Sending Postcards from a Plane Crash" is largely a studio creation, and was seldom played live by the band. Stump and Wentz had a particularly big fight regarding the track "Chicago is So Two Years Ago," which Stump initially did not want to record. He had secretly kept it to himself in case the band did not work out, and he wanted to pursue his own music, but O'Keefe wanted to introduce it to the rest of the band after he heard Stump singing it to himself in the studio lobby. Wentz disliked several lyrics, and he and Stump argued over every word one by one. The bridge features a guest appearance by Motion City Soundtrack frontman Justin Pierre. The band had wanted Pierre on the song but schedules did not work out initially. O'Keefe, who was friends with Pierre, recorded Pierre's part, which he wrote while the band was on tour, leaving it as a "surprise" for the rest of the group. "Grenade Jumper" references Christopher Gutierrez, who was an early supporter, and attended each show from the beginning. The song's chorus came from a conversation between Trohman and Stump in the kitchen of the band's apartment. Trohman said they should write a fan appreciation song, and Stump noted how Chris "was only friend". The song's title refers to a phrase coined by the band regarding "whoever would be the person that would have... um, relations Biblically with a girl in order to have the rest of the band stay at the house," said Wentz.