You can put on music that doesn't have DRM, such as stuff you've ripped from your cds, even if they're in your iTunes library. Hopefully they're in mp3 format rather than iTunes default aac. If you want to buy music downloads, Amazon.com sells all of their downloads as mp3s. Also, Amazon.com sells movie and tv show downloads that are compatible with your player. They do have DRM, however.
You can also get the DVR station and record tv. And if you can somehow figure out a way to copy your commercial dvds, you should be able to put the resulting video on it. Unfortunately, while it can be done and is done, I can't tell you exactly how to do it. It breaks the copy protection on it (decrypting), which violates US copyright law and we can't run afoul of the law on these forums.
Anyway, I forgot to tell you that you can burn your iTunes purchased music as an audio cd then rip that cd. You can rip it back into iTunes. Just make sure that your ripping settings are for mp3 rather than iTunes default aac. Then after you've ripped them, you'll have to clean up the tagging. Most/all of your song titles should be correct but your album and artist information will be lost.
If any of your music was ripped as aacs or you have iTunes plus songs, you can convert them to mp3. Make sure your default ripping setting is mp3. Make sure you have enough hard drive space because in doing the conversion, you are still retaining the original. Right click on the songs (you can do multiple songs) and then select "convert selection to mp3" or something like that. You will retain all information that was originally there.