Cool, I get to talk about a supplement nobody ever talks about!
One of the supplements Jennell did for JG was the Book of Treasure Maps. You know how the random tables in many games occasionally tell GMs to put a "treasure map" in a trove? What, are you going to just come up with one on the fly? No, it's going to take you time to construct. Rolling that result is an exercise in creating more work for the GM.
So, Jennell made a book with several "treasure maps" in it, each one with a location and encounters pre-built. Need a treasure map? Pick one you like from the table of contents and put it in a previously-unexplored part of your game world. Done.
Later, TSR tried to do the same thing with slick-looking products similar in name and scope, but for my money the scenarios in the original are fantastic, much better than any similar books.
I also appreciate the LARPers / cosplayers getting a photo on the cover.