Any module you purchase on Roll20 will have the maps that come with that module and the rules for the creatures used in that module. So for example, I buy module "X" and it has a creature from the Monster Manual. I don't need to buy the Monster Manual to use that creature. As a reminder, you can always purchase a module then refund it within 15 days. Roll20 has an excellent refund policy . This gives you a chance to purchase a module, check it out, and refund it if you don't want to use it. Warning: If you purchase an Addon make sure you check it out in a new game as the game will be deleted if you refund it. Add it to your desired game if you decide to keep it. Also, downloadable content (many image packs are downloadable) is not refundable unless it is damaged in some way.
