Eyewear & Glasses
You never look as cool as you can look, unless you're wearing a smooth pair of shades. It doesn't matter if it's night time, you're in costume, you can wear sunglasses no matter how dark it is. Take this opportunity to be fly, and get some eyewear or sunglass accessories. There are so many costumes that are incomplete without the proper eye accessories. Don't ruin your whole outfit by letting those peepers go uncovered.
What's a cop without his Aviators, or Harry Potter without his circular reading glasses? These are important parts of the get up, and you're just going to be going halfway without the proper eyewear. You don't want to feel naked this Halloween. You want to feel complete. You want to get all the right pieces for your costume, creating a costume monopoly. Don't be the Monopoly man without his monocle. Then you're just a man in a suit, who can't see well out of one eye.