Magician David Blaine, looking a little wobbly, stepped out smiling Monday morning from an underground coffin that he says was his home for seven days. When the three-ton water-filled tank that covered his Plexiglas coffin was lifted, Blaine sat up and looked around as hundreds of New York spectators cheered. "I saw something very prophetic . . . a vision of every race, every religion, every age group banding together, and that made all this worthwhile," Blaine said. He was buried 6 feet underground. Air was pumped into the coffin, but Blaine said he was given no food and received only 3 to 4 tablespoons of water a day through an intravenous tube. A plastic container and tube handled toilet necessities.