Encouraging creative writers to keep and maintain a commonplace book is always a fruitful exercise. Most of the “greats” had one (or something close to it), but contemporary examples like Eminem’s may be more relevant/motivating. Blogger and creative writer Austin Kleon has a digital version as an example. Colleen Kennedy has an excellent and creative class assignment relating to this as well.
Musician and producer Brian Eno and artist Peter Schmidt created a set of 100+ “creativity cards” which they entitled Oblique Strategies that can be useful to introduce to students and have them use over a semester. All the editions’ cards can be found via links here: http://www.rtqe.net/ObliqueStrategies/Edition1-3.html, but there are also websites, apps, and even printable cards.
And finally, speaking of cards, it can be fun to do experimental creative writing using index cards, a practice used by Vladimir Nabokov, Jean Paul, Arno Schmidt, Michael Ende, and many others. Open Culture has a short piece on Nabokov’s process.
Should you care to mine it for other possible ideas, I’ve got a digital commonplace of my own. Here are some possible places to start: