WWI Brass Trench Box -- Double-sided with mirror

Description

This is out of my husbands extensive WWI collection.  He says it is a snuff box.  Other sites on the net call it a pill box or shaving kit.
All I know is that it is sturdy, closes tight, fits in a uniform pocket and would keep all sorts of things safe in no man's land.
Made of brass.  There are no marks to let me know who made it or in which country.
The mirror is in really good condition, which is amazing to me.  The inside of the other side is coated with a black powdery substance.  Husband says he thinks it was originally covered with lead to prevent corrosion from the snuff.
The box itself only has one slight dent from being pushed closed again and again over the years.
2" x 3" x 1" approximately.