By limiting your definition of a GHB as only for urban commutes on mass transit you are telling guys like me that drive to find another acronym. A GHB is a bag designed to get you home in whatever situation you happen to be in. Some peeps like me don't use mass transit but we still need a GHB available, in our case we may only need to carry it one way and it might not have to carry any contents for the daily grind.

I commute in a small truck and use it as a base kit; it carries a lot and after a serious seismic event I can camp with it or use it to select items for a GHB. I'd never bug out with just a backpack, but getting home is something else.

Part of my truck kit is a Camelbak backpack with enough in it for an overnight. Your 10-12 pound limit is about right. Mine is closer to 15 lbs but that includes a full water bladder.

Some daily mass transit commuters may be limited to just what is in the bag on their back, others may have a drawer or cabinet in their office to keep supplemental GHB supplies.

Limiting this thread to only what is in Teacher's OP is fine if your goal is to carry your entire GHB on your daily commute; my goal is to have lots of options. I think we should keep the thread open to those options.