I have a GBxCart reader for backing up my games, which is juuuust the right size to also fit in a cassette case. I wanted to store it with my games, so I went ahead and also made an insert to fit the reader.

I also went a bit wild making J-card cover inserts for my games and tweaking in a series of templates for the j-cards. The template is available here, and you can get all the various game covers I ended up making here.