As to the "bag"portion of the GHB, if it is to be a true commuter or walk around the city kit, I suggest that you are best served by a small, low profile backpack. My current favorite is a black Tom Bihn Synapse,modified with Fastex lash patches sown on its bottom by my shoe repair shop and waterproofed by me. It's ~1100 cu. in. Plenty for what you're building, with room left over for lunch and a small tablet or book.
If you want mainly a commuter kit, one bag solution ( I.e. One bag for emergency gear and laptop/office paperwork), go with a North Face Surge II (or an analog), ~1800cu. in. of very well organized space. But, not so large as to be clumsy on a bus/train/plane commute. Suggesting same mod. as noted above. Additionally, take a black waterproof marker to the white lettering and reflective strips and it lowers the profile further and is very inconspicuous, even in a professional setting.