BOTH are at fault. "Compromise": The most powerful word for marriage! Seriously, in this case I think both parties share part of the blame. You need to either get rid of the box of stuff (e.g. get a shelf) or park your cars in the driveway (like 95% of the CA population) so you can fill the entire garage with boxes full of stuff!
George
PS: Just for the record: I have 2 cars in my 2 car garage! MY cars. My wife parks on the street!