And...to add a little comedy, here's Jack Black showing us 80 years of Halloween costumes (I know, he's on a press tour for the Goosebumps movie, and I'm assuming this is part of that). This one is slightly out there, a bit NSFW. Just so you know.
Lastly, if you're in a bind and need a Halloween costume fast, there's always this devil costume (below). I know this, because when my youngest was not quite 2, we decided to take him to a community Halloween party and--not having anticipated the party thing--I had to come up with a costume fast. I took a red headband I had lying around and a couple of pieces of red felt I shaped into horns and affixed to the headband. I dressed him in a red sweatsuit, took some red yarn and braided it into a tail with a felt arrow on the end (and just a couple of stitches to attach it to his pants). He was ready to go in just a few minutes. And as you can see, a red sweater works just fine.
Whether you dress up or not, go to a party (or not), or simply sit at home and enjoy the parade of children decked out in their costumes, enjoy the day!