Pulling together a last-minute costume is easy when you scout your closet for a few simple accessories. Better yet, choose a few you love from the small shops on Etsy and keep them on-hand for easy costumes year after year.
If your getup reflects a certain profession, adding an easy-to-carry tool of the trade can really boost your look. A hand-held sign reading "stop" or "slow" is just the right touch to a construction-worker look, while a utility belt adds a dose of authenticity to a police officer costume.
Horror and fantasy characters can also be helped by little additions to give them a boost of authenticity. A witch's outfit might benefit by carrying a broomstick. A mystical magic wand adds a dash of extra flair if you're dressed as a fairy princess or powerful sorceress. Carry a microphone with you as you show off your pop star outfit, or rock out with an electric guitar as a heavy metal singer.