In A Large Greased Roasting Pan, Combine The Popcorn, Cereals And Peanuts; Set Aside. In A Large Saucepan, Combine The Brown Sugar, Butter And Corn Syrup; Bring To A Rolling Boil Over Medium-Low Heat, Stirring Constantly. Cook, Without Stirring, Until Mixture Turns A Medium Amber Color, About 8 Minutes. Remove From The Heat; Quickly Stir In Vanilla And Baking Soda Until Mixture Is Light And Foamy. Immediately Pour Over Cereal Mixture; Stir Until Evenly Coated. Bake At 250