I'm going to annoy my brother so he cleans his car
Why are you so concerned about his car's cleanliness?
He left his snack packets in his car. If he's not going to clean it, I'll clean it myself by taking the garbage out of the car.
I can understand why you feel like he needs to clean. People should keep their possessions neat and tidy. It is his car though and you can't force him to clean up if he doesn't want too.
It just bugs me when I see the inside of his car full of junk.
Maybe if this is important to you, you can help him with it. But you shouldn't force him and you shouldn't do it alone.