A raw bar of the freshest clams and oysters dazzles cocktail guests with hardly any effort on your part. Use trays, large baking sheets, a zinc bar, giant clam shells, oversize copper washtubs, halved wooden barrels, or plastic-lined baskets, and chock them full of crushed ice. Sprinkle the ice with seaweed, fresh herbs, and wild flowers. Shuck the clams and oysters and arrange them on the half shell on the ice. Tuck shells filled with toppings here and there. Include Mignonette Sauce, Gremolata, minced tomatoes, caviar, lemon and lime wedges, spicy cocktail sauce, and minced chile peppers, and have a good many pepper grinders about.