Candles are always an option:
Wrap real veggies around them, hollow out gourds and place the candle in them.
Gourds or veggies are also good for floral as well.
Easier options for you can be to place fall themed vase fillers in a cluster of vases with candles. Clustering is very popular right now.
I hope this helps you in your centerpiece dilemma for you Thanksgiving table. Have a great Holiday.