To set starting equipment slot items for the player character go to the BP_PlayerInventory then in the class defaults search for starting equipment.

To add a new starting equipment item click the + icon then set the Data Table to MasterItemList. Next set the Row Name to the item you want to have added to the equipment slot when a new game begins. Then set the Equipment Type to the slot you want this equipment to be equipped to. The item will now be equipped in the set slot, if in the item list it is set to be a container and has starting items set it will contain these items.

Note – The item will only be added if it can be equipped to the slot set in EquipmentType.