Mix the Fritos, nuts and Crispix in large roaster pan. Combine brown sugar, butter and Karo syrup in saucepan. Boil for 1 1/2 minutes. Pour over the Crispix mix and stir gently. Bake for 8 minutes at 325 degrees. Stir gently and return to oven and bake for another 8 minutes. Spread on wax paper and allow to dry. (At least 2 hours) Add M&M's when cooled.