For just milling about, doing whateva, or maybe best to pull it out of the closet exclusively for Halloween. Well, in case you don't have a Halloween costume and plan on doing something on Halloween that would require a costume.
Lots available on Amazon as well, including this nifty unicorn mask:
By the way, reminds me of a little bad pun joke. What did the hat say to the hat rack? You stay here, I'll go on ahead.