Building a Portfolio and Gaining Experience

I thought having a lot of downtime between semesters would be really great (and it really is sometimes...) but as the days have started dragging by with infinite slowness I've decided it's high time to start creating a large portfolio for myself. You know, professional development and all that. 
While I've been applying for work experience, I haven't had much luck (the two I got hired for seemed to have... fallen apart... before I could even start. Just my luck.) so I decided that I shoul...