I remember when I was in the military, we had a lot of 20, 30, 40 year old equipment. For example, although the plastic water can was current issue at the time, we still had a lot of the old metal ones. We also had both the old black binculars and the rubberized green ones.
That's one catch with military modeling - some of the equipment that gets reused alot, like ammo cans and fuel cans, boxes & crates, etc, might be of a color or design no longer normally in service. A fuel can from 1938, for example, might be found on the back of a Panzer IV in 1944. Just because it isn't standard current issue doesn't mean it can't be used. Also, remember that some pics of German equipment show US fuel cans thrown in. Whatever will hold fuel.
Just make sure you don't use a piece of equipment that didn't exist yet, and be sure to weather the heck out of it. "Damage" it a little, take a dremel to it, or something so it looks well-used.
~J