I really liked the trick or treat bags idea, and spider pencil tops can be made using puff balls and pipe cleaners.
My girls always enjoy making their own jointed skeletons, using white construction paper and brads at the joints to make them poseable.
Each year we also make paper stencils to use to carve the pumpkin, draw the desired face and cut it out, Then trace it onto the pumpkin with black marker.
I have a body marker set we are going to use this year to design our own wash-off tattoos, you could have them create stencils and use washable markers, or maybe not if you are working with other people's kids...
When I remember any of the other crafts we did at halloween, I will let you know.