My thoughts are a bag with the essentials to live. Water purification, First aid kit, Matches, set of BDU's, Extra batteries, Good flashlight. Crank radio. P38.
I do not keep ammo or anything else related to that in my bag. Use a Maxipedition Versi pack (man purse) slung over the shoulder for that. If you get in a situation where you need to move fast you can drop your BOB and return for it after the threat is gone. This will lighten your load and keep you mobile and able to fight.
Good advice from Bronc! keep your weapons with you, under your control, with you, next to you, where you can feel their comforting weight. Close by always, closer than a backpack. Except for that "man purse" thing... can't we call it a survival kit or something?