Heat oven to 375°F. Spray 13x9-inch baking pan with no-stick cooking spray. Combine cereals, pretzels and nuts in prepared pan. Set aside. Combine brown sugar, butter and corn syrup in 2-quart heavy saucepan. Cook over medium heat, stirring occasionally, until mixture comes to a full boil (4 to 6 minutes). Remove from heat. Stir in vanilla and baking soda. Pour over cereal mixture in prepared pan; toss to coat. Bake for 10 to 15 minutes, stirring every 5 minutes, or until coating is set. Remove from oven. Stir. Spoon cereal mixture onto aluminum foil or large ungreased baking sheet. Cool 10 minutes. Break into pieces. Store in container with tight-fitting lid. TIP: This mix can be made ahead and stored in container with tight-fitting lid for up to 1 week. Microwave Directions: Prepare cereal and syrup mixture as directed above. Place cereal mixture into large nylon oven roasting bag. Pour syrup over cereal in bag. Shake well to coat. Microwave on HIGH, shaking every minute, until well coated (3 to 4 minutes). Cool as directed above.