Actually I think this thread is more appropriate in the General Mac section, so I'll move it.

Have a look at the Sticky at the top if this section & see if it applies to you. On OS9, sometimes the files are blank documents with white icons. Hopefully that thread sticky & its links will answer your question. Tell us how it goes.

mp3's, m4a, etc. should be fine for iTunes.

Videos - well Quicktime will play all types so long as you have the correct plug-ins (CODECs)

Softw. - Look for .SIT files, but you'll need to be aware of which versions are compatible with OS 9. You'll need to do your own research there.
You may find some bin files which are also meant for OS 9, but don't get confused with bin files used for windows CD image files.