In a large bowl, stir together popcorn, cereal, peanuts and pecans. Transfer to a greased roasting pan.
In a heavy 2 or 3 quart saucepan, combine brown sugar, butter, and corn syrup. Cook and stir over medium heat to boiling. Boil 5 minutes without stirring (make sure you boil on low heat or it will burn). Remove from heat and stir in vanilla and baking soda.
Preheat oven to 250 degrees. Pour sugar mixture over popcorn mixture. Stir gently to coat. Bake for 1 hour. Pour onto waxed paper and cool. Store in an airtight container.
I add M& M’s after it cools to make it an extra special treat! You could even add pretzel sticks if you wanted it more salty. Enjoy!