In a large heat-proof bowl, combine the chow mein noodles, cashews and peanuts; set aside. In a microwave-safe bowl, combine the brown sugar, butter, corn syrup and salt. Microwave, uncovered, on high for 2 minutes or until sugar is dissolved and syrup is bubbly, stirring frequently. Stir in baking soda; microwave 20 seconds longer or until mixture begins to foam.
Carefully pour over chow mein noodle mixture; stir to coat. Transfer to a greased 15x10x1-in. baking pan. Bake at 300° for 25-30 minutes, stirring every 10 minutes. Spread on waxed paper; cool for at least 30 minutes.
Place snack mix in a large bowl. Add candy corn and raisins; gently toss. Store in an airtight container.