Boy am I lucky! I already have the perfect backdrop for a Fall mantel! We found this painting in Canada and absolutely loved it! I added a few Fall leaves that the kids found last year (we pressed them), some grapevine balls, a copper kettle that I already had and a leaf dish.
In the Library, which dates back from 1789, there is a wonderful old fireplace which had an insert put into it years ago. In keeping with that design, I keep the lanterns on it all year round. I change it seasonally and now it is ready for Fall!
All of these pieces are in my house and I just rearrange them. All I added were the cornstalks and the garland.