Well we do that too.
Many of the coats that we use have interior, "invisible" pockets in the linings that can't be seen by the public, where folks carry things like car keys, cell phone, meds, etc. Some units for example, have good historic records, and these show either a coat without exterior pockets, or had pocket flaps sewn to the coat, but no actual pockets. (Military contractors folks - the colonel paid for the coats from unit money - any extra money saved by having cheap coats made..., the colonel pocketed. :grin: )
What makes a "military" coat is the "facings", the overlapping lapels, and some styles of cuffs. This isn't always true though, for the 60th regiment, raised in America, had red privates' coats without the lapels. The color of the collar and cuffs were different from the red coat (iirc they were black). NOTHING is stopping you from wearing a simple frock coat (no lapels and matching color cuffs and collar), and making it with a "cut down" skirt. While some units are listed as having an issued coat, coats were issued once per year, and if you joined after the issue and they had no extras to give you, you had to wear what you brought. Gorham's Rangers is one unit, and the Rangers at Fort Frederick in Maryland are another. In fact the rangers in Maryland aren't listed as having an issued uniform.
LD