Creative reminder checklists

David Allen says that there are seven types of things that need to be kept track of:

• projects
• project support material
• calendar
• next actions
• waiting for
• reference
• someday/maybe ideas

But then at the end of Chapter 7 of GTD, he suggests how useful it is to maintain plenty of checklists of creative reminders. So what are these? They don’t fit into any of the above categories, and he doesn’t say how or where there should be organised.