Easy is a pretty relative term. I know I can do that easily with the Inventory System but it won’t do it for you out of the box.
It can be easy for some and impossible for others. I think the hard part is coming up with a solid design and most of the work to achieve results like above is UMG/UI changes/logic (Jig Saw Slots).
I can think of a couple different designs to achieve that same result for storing items in tabs/clothing containers.
One way and probably the easiest is that you can setup your inventory so when you equip a backpack type item it gives you X amount of slots. Then you have the UI render a tab for this backpack type item and show how many slots it has. Because each backpack item will have it’s own assigned range of inventory slots you will know what items are in what backpack. Remember you just need to show the player the organization of the items in your UI. You don’t actually need to have items inside items inside complicated arrays. If they drop that backpack on the ground just spawn a item that looks like a backpack and put the items it had in it.
*(I can build a DayZ/Arma style UI using this method for the clothing containers. Weapons/Attachments and Clothing slots would be setup like the equipment slots are already a set of assigned inventory slots starting at 0)
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Another way is to create a backpack item that actually has a container type inventory. Then you can store an array of these containers which have some properties (Name, Slot Count, etc) and when viewing your inventory on the client loop through these containers and draw them to the UI in the way you want. This will require a bit more logic as you will want to handle a bunch of new container to container interactions.
The Inventory System is a great base to customize into any game style and to build upon for new features. The UI is Drag and Drop themed but that is just the demo UI. The Inventory System itself can be used with any type of UI design with a little understanding of how it reads the UI Item Data from your Inventory Items.
If you are looking for a more complete solution for that design posted above, I think there is another inventory system on the marketplace that does this more or less out of the box already.