My favorite holiday is Halloween. My Mothers maiden name is Casper, and we have lots of fun with ghost type things. I also am afraid of well, nearly everything. Somehow Halloween is a time where I can see the scary things and know how they work and they aren't scary anymore. But Halloween is the second least "green" holiday (Christmas with the useless presents, gift-wrap, and sparkly lights comes in first.)
What traditions are there? Kids get dressed up in costumes, only to be worn that day, and go around in hunt of way too much candy that is good for them wrapped in individual pieces. The sheer volume of waste from the candy is horrible.
So, either reuse old costumes, or get some that can be re-purposed into clothes to wear. Or make some out of your clothes. My favorite costume was a friend of mine who was Aladdin. He had a khaki pants of his, and a vest. He also had a mat as a flying carpet, and sang. I think it was the singing that made it. But simple and very green. Or, you could rent them. There are special Halloween costume rental places, or your local theater is going to have some that you could ask to rent.
I'm not sure what to do with the candy. I have recently been giving away toys instead. Not that this is any better, they probably are going to just throw it away anyways, but... I'm open to suggestions.