Our 3yr old ds is star wars crazy. We dressed our black lab up as darth vader (outfit borrowed from ds) she wore the mask over the back of her head and the black cape tied round her neck. She had the light sabre too but can't remember how we attached that.... Tho this outfit was only worn for ten min for fancy dress class at a fun show.
I went to a dog training class with my dog dressed as the christmas tree fairy, and wore a green coat with baubles pinned to it. She had a pale pink strap around her chest with netting 'wings' at the top, and a little frill like a tuttu around her neck.