A very well designed, useful military item was the good old E Tool short for Entrenching Tool.  It's a small folding shovel that fits in your pack.  Besides that it's a very useful weapon of last resort.  We even had a class teaching us how to use one in an emergency.  You  can slice, bash, or stab with it.  Also you can throw it like a throwing ax.

A friend of mine, a Marine and fellow survival enthusiast and I sometimes discuss what 5 items we would take on a longer term outing. He usually has E-Tool as one of his items.