I would get a joint gift, but gear it towards his taste and they can enjoy it together. He will appreciate your thought, and the bride won't kill you!
Maybe do a gift basket movie night thing with a card for a few movie rentals and popcorn, his favorite candy, and maybe a copy of a favorite movie he doesn't already own?
I also like the scarf idea, do his in a reference to a scary movie, his favorite color, or his name, but make one for the bride too. Hers doesn't have to be as fancy
If you want to do something decorative a decoupaged box would be neat, he could keep his things in it. Does he work in an office where he has his own space? Something decorative or functional could be made so it won't have to sit at home with his bride.