we helped a neighbor throw a great halloween party last year.
for decorations, we enlisted everyone to drop over (up to a week ahead of time) a jack o lantern for a contest (we did electric tea lights in them the nite of the party for safety). we hit up everyone for any spare decorations they might have (ended up with TONS). got a projector that attached to a laptop and projected old monster movies on the wall (dollar store has a ton of the old black and whites, also used netflix).
now we were doing this as a neighborhood thing, so no one person was providing all of the food-we did it potluck style and ended up with all kinds of stuff. if i were doing it on my own, i would still stick with the kinds of foods we ended up with-easy to prepare in advance: pulled pork and bunz, bbq beans, coleslaw, potato salad, chili (with chips and cheese for nachos, hot dogs and bunz for chili dogs), and a last minute item i brought for the younger set-several of the jack o lantern cheese and pepperoni pizzas from papa murphys. the main dessert item was (of course) lots of trick or treat candies, but ds and i also made a "grave yard" that was very popular-instant chocolate pudding mixed with oreos-absent the filling-then we got "gummy body parts"

that we made sure poked out the top. for headstone we got pepperage farms milanos, and iced them with white frosting tinged with black (ended up a nice gray)-then piped RIP (with selected adult neighbor names) on them

keep in mind-if you are celebrating on the actual holiday this year, since it's a sunday, you may have people not staying as long as they would at a standard party (esp. if they have kids that have to go to school the next day) so food consumption may be lessened, and if you are celebrating on saturday AND your community adjusts trick or treating to saturday as well, you need to reduce the amount of food the kiddies will eat (they consume the candy first if allowed), and the time the party commences (don't set it for a time where the parents have to choose between letting the kiddies trick or treat and attending the party during the period of time when the games/activities/feasting commences).