The stage show adds a perfect capper, after Flick has spent most of the show complaining about his "sore arm" from all the times Farkus has beaten him up.
Schwartz: Hey... isn't this your sore arm? Flick: Yeah. But it just started feeling better!
Mrs. Parker breaking the lamp and then telling the Old Man off about it.
Mrs. Parker: "That thing is the UGLIEST lamp I have ever seen in MY ENTIRE LIFE!"
What's even more awesome is that even after the "Battle of the Lamp", both Mrs. Parker and the Old Man buried the hatchet and went on with their lives together.
In the book In God We Trust, All Others Pay Cash (which parts of this film is taken from) Ralphie remembers his parents actually sharing a laugh over the whole thing sometime later.)
One exclusive to the stage show for Ralphie's classmate Helen (whom, as Ralph mentions in his narration, all the boys respect and are frankly a little afraid of). When Scut Farkus is chasing Schwartz and Flick through the neighborhood, he bumps into Helen and Esther Jane. He stares them down for a moment... and Helen stares right back, crossing her arms as if daring him to move any closer. He promptly gets out of the way and politely tips his hat, letting the girls go without any hassle.