On this page of our game guide go The Last of Us 2 we explain how to get materials, resources and ingredients required for crafting. Materials and resources are required to make disposable items, to buy passive skills, and to create upgrades to your weapons - all of those can make the game easier.
There is no proven or 100% reliable way to get large amounts of crafting materials - just try to explore all locations very carefully and look for items and containers (drawers, cabinets, etc.) where interaction icons will appear.
In the case of regular loot, remember that you need to acquire several pieces of a particular component (like rags), that is, to increase the number of this material by 1 in your inventory. It simply means that you can't produce new items very quickly in place of used ones.
You can slightly increase the chances of finding rare crafting materials and components. Supplements, which are required to unlock passive skills, can be found in various medical rooms or toilets.
Scrap is required to create and unlock weapon upgrades. It can be found in various locations like garages or even near the workshop tables.
Large amounts of crafting materials can also be obtained by opening safes which you can find in the game world. Locations of safes and descriptions of mini-puzzles connected with opening them have been described in more detail in a separate chapter of our guide.