Only Items that can be used can be pinned. The default Items that can be pinned/used are Weapons, Attachments & Items like Apple or Energy Drinks.
How can I Pin Items to the Favorite Pinned Menu?
If you want to pin a valid Item to the Fav Pinned Menu, you´ll need to do it from your Inventory.
Press "Tab" to open the Inventory.
Right-Click on a valid Item
Click on "Pin"
Press "Q" to Open the Fav Pinned Menu.
What happens if I move a Pinned Item Out of the Inventory?
When moving a Pinned Item out of the Inventory, either because you dropped it or because you stored it in a Chest or even delete it, the Item will be unpinned, ensuring no reference errors can occur.
What happens if a Pinned Item runs out?
If you use a pinned Item and on reducing the amount it runs out, it will be unpinned, ensuring no reference errors can occur.