On the ground I saw an ammo box. Since I had a full inventory I decided to carry it by hand while walking out of the military building to avoid running into others. While i had my ammo box in my hand i saw a canteen. I needed a canteen so i walked to it and used the TAB menu to double click on the canteen and moved on.

Moments later i noticed, when dragging ammo to the ammo box to create the space for it in my inventory, that the canteen was 'inside' the ammo box. I could take it out and use it.

I noticed that I could put everything inside the ammo box, including an ammo box, as long as it is carried by hand. {F29446}