My experience with SAR might be relevant here. I found that I needed to have a bag ready to go, RIGHT AWAY. When the call came, the requested response time ran from 'immediate" to "we will meet tomorrow morning at 4 AM." Thus my SAR bag had everything I would need to respond effectively to a situation where I needed to function unassisted for at least 24 hours. If there was time, I could fine tune the contents and modify my load, but that was not always possible.

Your GHB bag is analagous to the SAR bag. It should have what you need and should be capable standing alone. When a problem occurs, you might or might not have enough time to fine tune the contents with material from the EDC bag. Obviously, you will need to tinker with the contents to account for seasonal variation, if nothing else. You simply can't forsee the amount of time you will have to fiddle with bag contents in a real life emergency. That is why they are called emergencies....