I have played the game 5-6 times and feel like I have a strong grasp of the rules. I'm making a home brew campaign in an original chunk of space. Looking at all the decks, supplementals, etc. it is hard to know which materials will benefit running my campaign.
If you were starting out today what would be the #1 thing you would get to make your play sessions more effective?
Exclude CRB and Dice.