Add to your fantasy role playing universe whenever you can!
I encourage families to include not only the basic core rules in their collections, but the supplements too. You'll need to be able to come up with sudden/solo dungeon settings, wilderness settings, Underdark settings, extra planar encounters etc and thanks to Lankmar, throw together a city block or two on a whim as well.
Throw in the creatures unique to that world to increase your personal monster manual. Keeps repeat monster encounters down to a minimum.
Enjoy!