Treepad Lite: freeware Personal database, PIM, organizer, notes manager, text editor and search engine.
TreePad Lite (freeware) and TreePad Asia (freeware) are small and powerful personal database programs, only 465 Kb in size. They allow you to store all your notes, emails, texts, hyperlinks, etc. into one or multiple databases. With the look and feel of the familiar Windows explorer, editing, storing, browsing, searching and retrieving your data can not be easier!
TreePad can be run directly from a floppy, if necessary, including data. To find any article you previously created or imported, you can browse the tree, in the same way as you browse directories/folders in the Windows explorer. You can also use the internal search engine to find any piece of information swiftly.

I haven’t found many better ways of storing all the information about a campaign that you’re running. Unfortunately, the free version doesn’t allow you to store images within the tree. But that’s okay, it’s still a huge time saver, allowing you to keep everything organized within its own space, but easily accessible.