Marine tactics was another way to approach personal combat. I am guessing that most of our interpersonal combat training comes from marine instructors. They would know unarmed, knife, improvised and all sorts of firearms. The thing about firearms is not just being able to point and shoot but understanding the space available, how to move in it, arcs of fire, enemy reactions and how to manipulate them, use of grenades and breaching equipment, how to protect a fragile environment, appropriate equipment use.
But that is just one option. I personally have no problem going the GURPS route on having very specific skills, but I am also a fan of having relatively broad categories based around a type of training or life experience and saying “yes it it reasonable someone like that would know something about this”