One thing I would say before I get started is, don't get a cotsume out of a bag! Making up a costume can be half the fun, even if all it is is a few bin bangs taped together. Ready-to-wear costumes can be painfully expensive, and sadly are not always great quality. They're certainly not made for dark October/November nights!
1. Zombie-fy Yourself: This one is so, so simple. Grab some old (cheap) clothes that you don't wear anymore and cut holes in them, rip some seams and even tea-dye them in some places. Splatter with some fake blood, and your clothes are good to go! For makeup, green/white facepaint and fake blood are your friends. Make wounds everywhere, and even put fake blood at the edges of your nails to look like you've been doing some... digging.
2. The 'Cute/Nerd' Costume: Guys won't get away with this one I don't think, but girls can pull it off with flying colours. 3D classes with the lenses popped out, onsies and pigtails are all that is really required! Bonus: You're cosy and comfortable all evening.
3. The Joke Costume: AKA the 'pisstake'. You have lots of options for this one, just explore some characters from some of your favourite books, programs and movies. My personal favourites would be Snookie or Napoleon Dynamite! Just try to replicate their appearance as much as possible and you're good to go.
4. The Anti-You: Wear something that is completely out of character for you. For example, I don't enjoy wearing tracksuits or slapping on fake tan, therefore they would be what I would do to achieve the costume. A few ideas you may like are 'cholas', 'scene queens'. If you're going down the route of social cliques, though, I would stick to something that's gone a little.. old or stale, so no one is too insulted.
5. 'I'm Not That Bothered' Get-Up: If you're not feeling it this year and don't feel like wearing anything too extravagant, a LBD with some fake cobwebs draped over could do the trick. To link in more relevance to Hallowe'en, wear some more theatrical, dark makeup and maybe some fancy nail art!
I hope this has provided some inspiration to anyone out there trying to find a quick fix for tomorrow evening, and I hope that everyone has a wonderful time. Stay safe, etc..