interesting exercise.
The Christian bread and wine ceremony are actually far older than Christianity. The Roman and Greeks celebrated the harvest and the shaft of wheat and wine are symbols that are found on all sorts of artifacts.
Then there is the 'Children of the Corn' route. Human sacrifices to fertilize the fields for next years crop. Not what you had in mind huh? LOL
Another thought. At a workshop, someone told about someone who was oriental who savored every bite. It made everyone late on their planned schedule, but the guy would not be rushed in his almost religious style of eating.
On Star Trek, they kept ringing a gong right?
Honoring the four winds before eating is native American, I believe.
Pioneers collected the prairie grass seed, and would dance in the seed. I think that was fall.
Barn Dances and BBQ on long tables.
A part of the first crops dedicated to the gods. (Probably several early cultures.)
My rural roots are showing none of those are metropolitan. Fall isn't fall until my first symphony or orchestra. Music as a backdrop to the meal.
Anything with pumpkins... pumpkin pies, pumpkin cake, pumpkin & squash soup.
In Italy there is a town that puts the fresh wine into the town center fountain for common consumption and enjoyment.
uhm, my others ideas are getting into the hunting/butchering stuff. Again not what you had in mind.
The Baldwin boys play football with the frozen turkey. LOL
Pioneer weddings had all the guests bring a round layer cake. Then they stacked them up with frosting.
How about the practice of drying flowers. Usually they are cut, tied together in bouquets and then hung upside down in a dry dark place. You could use them overhead on some sort of awning over the table. It would smell great!
How about a simple potluck? That has to be a practice back to the Neolithic era!
Necklaces made of fall flowers?
Food that is not freezable, nor able to being dried, that would be a special treat only available immediately after harvest.
Someone else can pick it up from there....