They do not have to be your original content, but you must have permission to distribute everything in your module. This includes rules, art, music, story, etc. As an example, I am not a very creative person, but I am good at making high-quality Roll20 modules and cleaning up art assets from PDFs. I secured licenses with royalty agreements with publishers to distribute their adventure modules and other content on Roll20. If your story is original, but everything else is not, you have a few options: Rules: 5e and Pathfinder both have licenses you must follow to release content using their rule sets. Tokens: There are several royalty free packages of fantasy stock art on DriveThruRPG. You can also look at Pixabay for CC0 content. Maps: Again, you can look at DriveThruRPG. There are also a few programs that let you draw your own maps (and I believe give you permission to use the end product commercially). Music: There are a few music options available. Incompetech has a royalty-free Creative Commons attribution license for almost all of his work. It even comes with a generator to properly write the attribution text. I hope that helps, and let me know if you have any other questions.