Halloween costumes as a whole are not very green. Whatever material used to create them is used only for one night and then usually, especially if elaborate, the whole thing has to be thrown away. Costume rentals eliminate this conundrum. Or, like my husband, wear the same battered wig every year...

Have a friend dress up as a tree, put on your best hippie outfit, and when someone asks what you are, give your friend a hug.

My friends and I have amassed a large amount of costumes over the years.  So instead of buying new ones, we're borrowing from everyone else's costume box.  It saves money and is eco friendly!

Halloween parties for adults..., well- if you are planning to go and have a good time, this is the time for you to show your reuse-ingenuity! Ditch the buying a [probably imported from afar] premade costume- look in your own closet, your recycling bucket, etc. Way back 'in the day', one of the creepiest-looking ways to make up our faces was also considered good for the skin- Rub honey on your face & stick dry oatmeal on it! This is especially creepy in a darkened room with a flashlight stuck under one's chin (light beam pointing up). Substitute granola for the honey, and you can go as an environmentalist cliche. Obviously, your clothing should be washable...

I dressed up today as a CFL lightbulb...just stuffed tube socks and pinned them in a swirl to a white shirt. I won 4th prize at work (I do work for a recycling company...) All thanks to your ideas, Umbra :)