What did Bud have to promise to tell Herman after eating in "Bud, Not Buddy"?
After eating, Bud has to promise to tell the truth about why he has come to the band, and the circumstances that are leading him to claim that Herman is his father.
Bud has managed to travel all the way across the state of Michigan on his own in search of Herman E. Calloway. What Bud has already told the band about his mother's death, his escape from the foster home, and his belief that Calloway is indeed his long-lost father is the truth as he knows it, but the story is unquestionably far-fetched, and the members are not sure what to believe. It is actually Jimmy, not Herman, who senses that Bud is starving, and makes him promise "to be straight with (them)" once he "get(s) something in (his) belly". Herman himself is completely skeptical of what the boy is claiming and has already made up his mind that Bud is lying. Herman tells Jimmy, "Well...like I said, if he's gonna be doing some explaining it's got to be to you, I don't need to listen to this scamp's nonsense whilst I'm trying to digest my supper" (Chapter 13).