Back in the 1990s, when TSR published a campaign setting, they usually went the whole nine yards regardless if whatever they produced was usable or not.
A Player’s Primer to the Outlands is a case in point. The big attraction here is that it came with a CD with over 41 tracks for your Planescape campaign.
The premise here is that your players have come across a talking skull and are supposed ask it questions about the Multiverse–specifically the Outlands. And then the DM is supposed to play a track.
Most of them are entertaining. They tell a story. They share some information, and if your players are tromping around the Outlands you’ll find some use for this product.
You can find a number of them at this YouTube Channel.
They’re also available for download in the Wizards of the Coast archive (provided you have the right kind of software to play them. https://www.wizards.com/dnd/article.asp?x=dnd/dx20010914a