How Do I add Floor loot to my creative map?

I am making a game mode and would like to put floor loot in it.

I would go with Item Spawner device.

In your Content Browser, go to Fortnite → Devices and find Item Spawner, add it to map. Then in the Item List of that device, add the item(s) you want to appear on the map. Turn off “Base visible during game”.