Grease/spray a 9x13 pan. Measure cereal and pour into large bowl. In a large soup pot, melt marshmallows and butter together until smooth and creamy, stirring occasionally. Pour cereal into soup pot, and stir until well coated. If you're soup pot isn't big enough you can pour the marshmallow mixture over the cereal in that big bowl, but then you have two sticky marshmallow pans to clean, so if your pot is big enough totally pour the cereal and save yourself some scrubbing! Stir in marshmallow bits and chocolate chips at the very end when the marshmallow mixture has cooled a little. I like to freeze the chocolate chips if I have time, but if not, I wait until the absolute last second and stir quickly so they don't melt completely away. Spread mixture into prepared pan. Cool and cut into bars. Enjoy!