If you're serving family style, guests can stake out their seat by placing their plate at the table when they arrive. Buffet style? Encourage stacking plates at the start of the buffet and everyone using each others. What would be more in the spirit of sharing and Thanksgiving?
Sure, your table isn't going to end up looking like a page out of a magazine (or will it?). But everyone will have contributed and the warmth of each guest's home will be present around the table.
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(Images: Outstanding in the Field; Daily Mail via Re-Nest)