Heat oven to 325 degrees. Butter jelly roll pan, 15 1/2 x 10 1/2 x 1-inch. Heat brown sugar, corn syrup, margarine, and salt in 3-quart saucepan over medium heat, stirring constantly, until sugar is dissolved, about 5 minutes; remove from heat. Stir in cereal and nuts until well coated. Spread mixture in pan. Bake 15 minutes. Cool 10 minutes; loosen mixture with metal spatula. Let stand until firm, about 1 hour. Store in covered container. About 8 cups snack.