If you're throwing a Harvest Celebration, then you're probably planning a few outdoor games.
Why not try Gourd Bowling?
Or "Pop Goes the Pumpkin"? While this photo looks like it may have been taken indoors, I would highly suggest that you make this an outdoor activity, as it involves glitter.
Maybe some Croquet?
Last year, we had a Harvest Celebration Dinner with our friends, but this year we're opting for a more low key celebration. Very low key . . . it will just be the two of us. The night will consist of delicious food, Autumn themed cocktails and a few games. Nice and quiet!