Understanding what package files are and how they work is the first step in your modding journey. These files allow you to add new items, modify existing ones, or even introduce entirely new gameplay elements. They are like the DNA of your creations, containing all the necessary data and information. Package files are the bread and butter of custom content in Sims 4. VIEW ALL (4) VIEW LESS The Building Blocks of Sims 4 Custom Content Understanding the Basics of Package Files Conclusion: The Joy of Creation in Sims 4.The Building Blocks of Sims 4 Custom Content.