Thanks to a response on a discussion thread under Wirecutter's backpack article, I think I've found a strong contender:

eBags Professional Slim Backpack

Looks like it has lots of vertically aligned pockets and compact size. Looks good.

I forgot to mention that for the moment, I just ended up getting a packing cube type thing for my back, I have flash drives and some cables semi-organized inside it. It's awkward to put in the bag and to use, though.