The World Builder's Guidebook lists the following components to a GM's notebook
Maps of the world, continent, kingdom, city, or adventure region, as required.Character sheets for all major NPC's.A log or short form for minor NPC's.A record of adventures, including treasure found, character developments, and foes overcome.Up-to-date copies of the character record sheets for all the player characters in your campaign.A collection of special notes, rules changes, new items and spells, and similar "customized" touches for your campaign setting.Photocopies of stat sheets for any unusual monsters picked up from other sources or designed for your campaign.Notes on the calendar or passage of time, if you track time in your game.A tickler file or wish list for the PC's, noting the motivations and long-range goals of each PC (very useful for designing adventures your players will want to take part in).
A fairly extensive, but not unreasonable list. The classic way to do this is with an actual folder or notebook that you lug around with you. A more modern take would be to use a site like Obsidian Portal or a locally hosted wiki (or just keep your files all in one folder or the like). Since I don't know if I'm going to run this game on-line or in-person, I'm leaning toward an actual physical notebook and/or just a collection of various files.Notes on the places and sites of interest in your setting, including major NPC's, adventure opportunities, local customs or societies, and anything else you might find necessary to describe a region
In order to make the act of creating the notebook as well as detailing each area, the WBG includes a number of blank sheets. A good number of these are generic hex and grid maps, but there's also forms for detailing Kingdoms, Areas, Towns, as well as specific sites. Fairly similar to the later One Page Dungeon idea. Basically, you have all the relevant information for any given area on one convenient page.
But I have some issues. First, the copies of these forms on the PDF I have aren't the cleanest (and over the years I've of course lost the pad that came with my book). Two, my penmanship is utterably horrible. Three, and closely related to two, I really don't have a gift for drawing my maps out. Which is why I'm using Campaign Cartographer for my mapping needs.
So, instead of trying to these by hand (the way I'm certain God and Richard Baker intended), I going to try and do these on the computer, most likely in Word/OpenOffice. I'll import my maps from CC3, so I still have all the information I need in one nice single page. I'm not going to post all of these, since there is no super easy way to covert a Word document into an image (I'd have to print it out and scan it, or follow these steps and screw that). But, I do want to share my first pass at this template, the kingdom overview for Galicia.
It's not terribly pretty looking, but its for the GM's eyes only. Also, it's black and white, since I had to print it out and scan, and I don't have my color printer/scanner readily available. I'll be creating one for our general wasteland area, one for each of the villages, and then, when I finally get to adventure areas and the like, one for those as well.