I would use a separate backpack. Why? Easy on/off. I wouldn't want it to weigh me down or fuss with it in transitional spaces, if a self defense situation popped off. Drop the extra bag and you're in the fight. I'd point to modern troops as an example. Only have the bare necessities (IFAK, cantine, fun sticks and pouches, tourniquet, light, cutting/multi-tool, firestarter, and a COMM like your cell phone) tied to your person or uniform. Everything else can be dropped and picked up again after the dust settles.