Hi Matthias D.D.! The official modules will give you all of the monsters, magic items and spells you need to run the adventure, included in the module. No additional purchase necessary. However, that info is very handy to have if you like tinkering, your players get creative or run off the rails a lot, or you want to give them access to things not in the module (character building rules, for example). I'm not terribly versed in what is freely available for PF2, but if you have not purchased the rulebook yet, creating a game using the official PF2 sheet will hook you up with the PF2 compendium at the free level, so you can see what is available without purchase. Keep in mind, that if you buy the module, the monsters will all have artwork and tokens, if it is in the module book or the core rulebook. Also, special rules that are normally only in the rulebook, but are referenced in the adventure are typically included as handouts. So if the adventure relies heavily on survival rules, those would likely be in handouts in the module. Hopefully a PF2 player can chime in with more detail, but that's the general policy.
