I taught Creative Writing several years ago and found that students were stumped on where to find stories. I had them write an "I remember..." list (very Lucy Calkins of me) for which the instructions were 1. Don't stop writing and 2. Don't think. That unlocked some good stuff and then I'd give them five minutes bursts in which to write what I called Verbal Sketches (I used a self-deprecating Dieter from Sprockets accent when I used that admittedly pretentious phrasing). The rubric for the assignment is long gone, but a good portfolio really should be wildly open-ended, no? Hope this helps!