Dig a shallow pit in the sand and line with large stones. Gather driftwood from the beach and pile on top of the coals. Create a bonfire by burning the wood for 1 to 2 hours until the rocks are red hot. Rack off the ashes. Set 1 cinder block on each corner of the pit to form the base. Lay a barbecue grate (or a piece of steel) on top to make a table. Gather seaweed from the beach and place a thick layer on the metal.
Place the potatoes and corn on the rack, then cover with a thin layer of seaweed. Mound the lobster tails, claws and kielbasa evenly on top, then cover with another thin layer of seaweed. Set the clams and flounder on top and cover with another layer of seaweed. Finally, set the oysters on top, then cover with a thick layer of seaweed. The juice from the seafood will drip down and flavor the corn and potatoes. Cover the entire bake with burlap or a tarp soaked in seawater. The tarp traps in the seaweed steam and bakes the food. Keep the tarp wet by pouring seawater over the top if needed. Cook until the clams open and the lobster is bright red, about 1 to 1 1/2 hours.