Grease a 9-by-13-inch baking dish with cooking spray and set aside.
Melt the butter in a large saucepan over medium-low heat. Add the marshmallow spread and cook, stirring frequently, until the butter and marshmallow are well blended, 3 to 5 minutes. Turn off the heat, add the rice cereal and graham crackers, and stir until well combined. Immediately fold in the chocolate chips.
Press the mixture into the prepared baking dish and let cool until set, 3 hours at room temperature or 30 minutes in the refrigerator. Cut into 1 1/2-inch squares. Thread the squares onto metal skewers, 4 squares per skewer. (If it's a very hot day, stick the skewers into the freezer for 30 minutes before toasting.)
Broil the skewers or roast over a campfire for toasted s'more deliciousness!