I've only ever been through college and the post-college job hunt (ok, during college job hunt) once, so I don't have enough data to form even a line, but my experience is that everything I did outside of actual classwork ended up being the most important parts of getting a job. If you only do the assigned classwork, then when you graduate you'll be competing with however many students are in your class who also did the same projects and learned the same skills. If you do something outside of the curriculum you'll stand out from your classmates for anybody looking for your particular skills.
Developing some software or even a useful web page will also help a ton once you get past the HR drones. It doesn't have to be the next Google, but having something to show the people you'll be working with is a huge help. Open source projects are great for this.
The final note: Don't think you have to do all of your partying in College because you'll be a family man the instant you graduate. Unless you are one of those guys who immediately has kids after graduating (or before!), there isn't nearly as much difference between college life and graduate life as movies/tv/etc... would make you think. This means it's ok to miss some parties because you're working on your cool side project. Just don't miss all of them because making friends and having fun is important too. It's a really hard balance and we don't make it easy on kids by giving only ridiculously one-sided advice that doesn't pass the real world test. I will say that you will regret it if you party too much and have to take a year of school all over again. Student loans suck big time. Oh, and paid internships/co-op opportunities that let you avoid having to take big loans? Solid gold.