1. Place two ammo crates down.
2. Use the attachTo command on the 2nd crate to attach it to the 1st crate.
You can remove items from crate 1, but not crate 2.
You can place items from your inventory into crate 2 but not crate 1.
You can still place items into crate 2 but not crate 1.
You cannot take any items back after they have been removed.