Military crossbody bags are made specifically to house arms and equipment without impeding on other pieces of gear and protecting what is inside from impact or elements.
Yes. Aside from military applications, combat bags are ideal for storing civilian job equipment such as laptops and tools, as well as camping gear and side arms.
Not by itself. It is, however, illegal to pretend to be a veteran or an active member of the military by wearing insignia or commendations that you haven’t earned.