Pre-heat oven to 250. Spray 2 large baking sheets with PAM.
Mix cereal, popcorn, and peanuts in a large bowl or pan.
In a heavy saucepan, combine margarine, brown sugar and corn syrup. Bring to a boil over medium heat, stirring constantly. Boil for 5 minutes without stirring.
Remove from heat and stir in the vanilla and baking soda. Mix will get frothy as you stir.
Pour over cereal mix and stir to coat evenly. Turn onto 2 large baking sheets.
Bake for 45 minutes, stirring every 15 minutes. Cool completely. Break apart and add your desired mix-in's. Store in airtight containers.
Mix-In's -- Make your mix-in's fit the holiday. Use as few or as many as you like. Don't choose anything that would make the cereal mix absorb moisture and become soggy, e.g., mini cream filled cookies.
Suggestions for mix-in's - mini Hershey Kisses, mini peanut butter cups, nonpareils, malted milk balls, other small chocolate candies, M&M's, chocolate and white covered pretzels, mini cookies (not sandwich-type), animal crackers, grammy bears, goldfish cookies, candy corn, etc.