I usually keep my Midori passport in my handbag. I use it for notes, but because I also have the pocket inserts, I always have stamps, and those cards for doctor's appointments in it, too. The notebook I use for notes about books I want to read/buy (esp. when I am in a bookstore or reading BookPage)--I get books from the library rather than buy them. Occasionally I come across a quotation I want to take note of. If I want to vent or something, the notebook is there.

I do carry a Nock Sinclair and put some of their index cards there. Those are mostly to give to others if I need to write something down for them.