In a small sauce pan, over medium heat, melt butter. Pour cereal into a clean brown paper grocery bag. Add sugar and corn syrup, stir. Bring to a boil. Boil for 1 minute. Pour caramel over cereal, and roll bag closed. Shake. Place bag in microwave and cook for 1 minute. Remove and shake again. Microwave 2 more times for 1 minute each, shaking between. Pour Crispix on to a cookie sheet or wax paper to cool. While cooling, stir cereal several times to prevent from hardening together.