He found Duke Nukem 3D , The Oregon Trail , and obscure Japanese RPGs translated by fans. He found a folder labeled /DOOM_WADS/ containing hundreds of fan-made levels.

To build a stash that functions completely offline, you must collect games that do not require digital rights management (DRM) handshakes. GOG (Good Old Games)

Here is a general roadmap to creating your own ultimate stash system:

Your "ultimate stash" needs to survive hardware failure. Follow the 3-2-1 backup rule: Keep the original and two backups.