There are TONS of sites you can Googles for awesome ideas, especially for foods.
For a kids halloween party several years ago I made a kitty litter cake and the kids LOVED it! I know that can be Googled, too, and it was so fun to make. It was delicious to eat, too!
I remember one were there was cooked spagehtie for brains, pealed grapes for eye, others stuff. We sat in a circle in the dark and put our hands in this stuff. It was gross. By it is halloween. Good luck that is a hard age, tweens.
I think this site has a lot of good ideas.
Last year for our halloween party invitations, we took tootsie pops and put square piece of white cloth around sucker part and put a ghost face on them. On the other side of the cloth we wrote info about party. Anyways they were really cute, but our party consists of younger kids so I don't know if that would be cool enough. lol