There’s not much to a good convenience store — snacks, lottery tickets, a few home necessities, maybe birthday cards. “Kim’s Convenience,” now running at Princeton’s McCarter Theatre, explores the unique power of a convenience store to fuel an immigration story. These are serious challenges and conflicts, but “Kim’s Convenience” approaches them all with humor that grows mostly from the bombastic and gregarious Appa. The show is often laugh-out-loud funny, but Choi still invites audiences to recognize how Appa’s love can bruise and scar. Like a small but surprisingly well stocked corner store, “Kim’s Convenience” is a short but markedly rich play.