You can tell a lot about a literary character by what's in their pockets. Or in this case, what's pinned to their coat. In Babbitt's case, the most important item is the button saying that he's a member of the local Boosters' Club, which is an organization for businessmen to pal around and talk about… well… business. Yawn.
As we find out through a direct description, the Boosters' Club button,
… made Babbitt feel loyal and important. It associated him with Good Fellows, with men who were nice and human, and important in business circles. It was his V.C., his Legion of Honor ribbon, his Phi Beta Kappa key. (1.4.23)
In other words, there's nothing more important to Babbitt than being part of respectable society. Scratch that. There's nothing more important than being seen as part of respectable society.