Poor Ron. All his best subplots in this installment got cut on the journey from page to screen. This was Ron's year…at least in the book. He was supposed to be named prefect and win the House Cup for the Gryffindor Quidditch team, but alas: the movie cuts all that.
Hey, he does get to stand up to some Slytherins though:
HERMIONE GRANGER: How'd you get away?
GINNY WEASLEY: Puking Pastilles. It wasn't pretty.
RON WEASLEY: Told them I was hungry, wanted some sweets. They told me to bugger off and ate the lot themselves.
HERMIONE GRANGER: That was clever, Ron!
RON WEASLEY: It's been known to happen.
Ron also gets to pretend he doesn't have a massive crush on Hermione every time he asks her to do his homework. He even tries to save her from Grawp, but she handles it with her firm lady voice. Dude, we see right through you. Just give it a couple more movies and love will blossom on its own.
So if most of Ron's character development got cut, what exactly is his role in this movie? To stand by Harry like a good friend. When Harry want to talk about girls, Ron is there. When Harry wants to yell at someone because he's just so angry and alone, Ron is there. And when Harry wants to rush off to the Ministry of Magic and fight Voldemort? Oh, Ron is definitely there.
Hey, that's what best friends are for.