During the index-card-a-day challenge there are always SO many cards flying. Ideas prompt more ideas which take other ideas for rides and once you get started you'll be propelled into idea-land. I know it probably doesn't make sense unless you have experienced idea-land. Get a stack of index cards, start with one idea, and let your mind wander and see what happens.
So I'll volley this over to you. What are you curious about?
Paper marbling, weaving paper, origami with index cards, drawing mandalas, drawing maps, brainstorming, using all of those postage stamps and patterned paper you've been collecting for(ever), drawing diagrams, carving eraser stamps, moving paper around the page, sketching people at the coffee shop.