First idea, backpacks! :D
You should be able to find bigger backpacks that would be able to carry more loot!
2nd Idea is crates, but have the crates be locked and you will need one of idk maybe 5 keys, so if you find a locked crate you will have to have the right key! :D Also make the radius a lot smaller to place walls and doors next to each other. Final idea is make it so you can put locks on doors and you will have to type the right word to open the door! :D thank you and take care!