1. Preheat oven to 350°. Combine cereal and next 2 ingredients in a very large bowl.
2. Melt butter in a 3-qt. saucepan over medium-low heat; stir in sugar and corn syrup. Bring to a boil over medium heat; boil 2 minutes.
3. Pour butter mixture over cereal mixture, and stir quickly to coat. Spread in a single layer on a lightly greased aluminum foil-lined jelly-roll pan.
4. Bake at 350° for 10 minutes. Transfer to wax paper, and cool completely (about 10 minutes). Break into pieces, and toss with pretzel sticks and chocolate pieces.