After several years of slimming down the merchandise mix to make stores less cluttered, retail chains including Dollar General, J.C. Penney, Old Navy and Wal-Mart are packing products onto walls, shelves and even aisle floors to boost sales. The earlier trims came in response to customers' calls for less-cluttered stores. "They loved the experience. They just bought less. And that generally is not a good long-term strategy," said Wal-Mart's U.S. CEO, William Simon.