Symbolism, Imagery, Allegory
If you're anything like us, you hung on to some childhood trinkets for way too long. Maybe it was a "Everyone's A Winner!" tee-ball trophy, or a crown from an elementary school play. And, at some point, you realized that getting your adult life started meant finally throwing away your kiddie nostalgia pieces.
That's pretty much what happens with the battle royal briefcase... except that particular piece of luggage is weighed down with societal expectations and racism as well as youthful innocence.
We think it's symbolic that the narrator receives the briefcase as a naïve kid, and then hangs onto it for the rest of the novel. Emblematic of his past vulnerability, eagerness to please, and youthful ambitions, his final loss of the briefcase suggests a complete severance of ties to his youthful past and a true rebirth.