I would set up a dynamic inventory system for both your player character and the loot containers. That way, you are not limited on slots for either container. (i.e. if you wanted to use a container to store items from your inventory).
This is a good tutorial on dynamic inventories, crafting, and stacking. Create a Crafting & Inventory system in Unreal Engine 4 Pt 2: Pickup logic & Add Items to Inventory - YouTube