I ordered a memory expansion from Go4Retro. This device has 8MB flash space. Enough to store all games ever published for the VIC-20. I flashed an image with most games and some utilities, available on the maker's website. This image of about 4MB took 3 hours to flash. Of course this is done on the VIC itself. You can use sjload to speed up it a bit.
The expansion allows you to flash your own "cartridges" and customize it completely.