Don't fall for conventional Thanksgiving centerpieces, they are so overdone by now that they only elicit groans.  Think of side issues to Thanksgiving, like Indians, puritans, fragrant small green branches with pine cones, candies and artificially made fruit.  Cornucopias spewiing grapes are awful, Indians with grapes? I doubt it.  The branch idea has the benefit that people can see each other over it and you can also add small glass enclosed candles.  Get scented candles but subtle smells and outdoorsy.  After all they ate outdoors, right?