I have two Lowpro bags, one small one large. The small one is just fine with a belt to wear around the waist for short trips and city stuff.  For trecking, I would need something more like Danny has.  The large bag for me is to travel with and hold the gear, not for the woods, more like a suitcase and not a travel baq.  Best wishes in finding what you want and may it be comfortable to wear.