Anson Mount was originally reluctant to play Ben, but was encouraged by Robert De Niro, with whom he was working at the time on City by the Sea (2002), who turned out to be a huge Spears fan. They went over scenes on break from "Sea", with Mount reading his role and De Niro reading Britney's.
At one point in the movie, the girls sing "Bye Bye Bye," which was a hit song by N'Sync. This was an inside joke referencing the well-publicized romance between N'Sync member Justin Timberlake and Britney Spears.
No Coca-Cola products are ever used. Instead, Pepsi products are featured prominently, e.g. Mimi drinks from a Pepsi can in the hotel room after their karaoke win. Britney Spears, of course, endorses Pepsi-Cola.
Bowling For Soup, the band who features in the film and have 3 songs in the film, belong to Spears' record company, Jive Records, as do *Nsync (the band featuring Spears' then boyfriend Justin Timberlake) who also have a song that features in the film.
In the scene where Mimi, Lucy and Kit are partying in the Louisiana Hotel room, you can hear Britney Spears accidently shout "Zoe" at Kit played by Zoe Saldana when they are laughing about a dirty subject.
Dan Aykroyd created a detailed back-story for his character and his life in the navy. He even had a friend draw a navy tattoo on his arm (which can be seen in the scene where he is working on the car in the garage).