Ask HN: What's missing in a CS degree?

There seems to be lots of post both recent and before discussing the inadequacies of a CS degree. Could anyone elaborate on how to fill up this gap for better preparation in the real world? What would a person who wants to start a start up need to learn on his or her own? Also, what about open source contribution. I realize most answers would probably follow along the lines of "work on your own projects." but I would like more detailed advices based on your personal experiences. How much work is there left when just out of school? What did you do to fill that gap?