Set oven to 350 degrees.
Line two baking sheets with foil and lightly coat with cooking spray. Divide cereal, pretzels, pecans and mixed nuts between two pans. Set aside
In a medium size pot, melt butter. Add brown sugar and light corn syrup. Stir and bring mixture to a boil. Turn down to a low boil and cook for four minutes. Pour half of mixture over each pan of snack mix. Using a nonstick spatula or wooden spoon, mix to coat dry ingredients. Place in oven and bake for 8 minutes. Remove pans from oven. Toss snack mix. Return mixture to oven and cook for additional 8 minutes.
Remove from oven and let snack mix cool completely. Break apart any large pieces. Store in an airtight container for up to one week.