Inventory Hot Bar
Gun, Joints, Radio, Food, Drinks
Your 1-5 Keys (not number pad) is your Inventory HotKeys. Putting items from your inventory in those slots will allow a quick press to use without opening your inventory.
NOTE: You need to put your weapons in a HotKey Slot to pull them out or put it away.
You also cant give someone an item from your HotKey, you need to move it down to a normal slot and then give it.