I have found at that age they really like nibble food and pizza is always easy. If you make your own pizza you can cut the dough into coffin shapes.
Take some cookie cutters and cut out flour tortillas, spritz with butter flavored Pam and sprinkle with cinnamon & sugar, bake until light brown.
Cheese quesadillas - using the cookie cutters to cut out ghoulish shapes.
Add green food coloring to dip w/ sliced veggies. Cut cucumbers into coffin shapes, carrots like swords etc....
Cheese ball covered with whole black olives - put some cream cheese in the center of the olives like eye balls.
Grapes, apples & marshmallows with a peanut butter/whipped cream dressing makes a great eyeball salad.
Murky Punch:
Mix equal parts 7-up & Apple juice add a couple of tablespoons of lemonade concentrate with some green food coloring. Place gummy spiders, worms etc in bowl. Cut off a section of the gummy to get a sticky spot to stick to the glass. Freeze gummies, plastic spiders etc... in apple juice for the ice floats.
Have fun...........