Prepare a baking dish and a large mixing bowl with non-stick cooking spray. Pour cereal into a large mixing bowl and set next to your stove.
Heat caramel bits and butter together in a large saucepan over low heat until both are melted and the mixture is smooth, about 5 minutes; add marshmallows. Continue to cook the mixture, stirring regularly, until the marshmallows are melted and the mixture is smooth, about 5 minutes; pour immediately into the middle of the cereal in the bowl and quickly stir to coat cereal completely.
Spread the coated cereal into the prepared baking dish. Spray the back of a spoon with cooking spray and use it to press the cereal into an even layer. Let cereal cool completely before cutting into squares.