Timbuk2 Classic Messenger: how much can it hold?

As with wallets, I'm always on the look out for a good, small, lightweight bag. Day-to-day, I use a Solo Universal Sling which perfectly fits a MacBook Air 11", iPad Mini, some business cards, pens and - when needed - the laptop charger:

The bag's definitely small (a few extra millimeters of length on the MacBook and it wouldn't fit) and weighs only 380g. No extraneous weight: very happy. It looks alright but isn't perhaps as professional as I'd like, and a sleak/small backback would look better and be better to carry for longer periods. But, as a commuting bag for day-to-day travel, it's fine.

However, sometimes I have to take overnight flights. Usually I try to travel with just a small carry on roller suitcase and my laptop bag, but when big suitcases are in the hold or I want to be able to quickly stash/access a hoody or sweater, a larger travel bag is useful. After some Googling, I decided on a Timbuk2 Classic Messenger Bag (medium). This isn't a full review, there are plenty of those on the Internet, but I had real difficulty trying to find out how much it could store. The answer is "plenty":

Certainly the medium size would be far too big for a day-to-day laptop bag for an 11" MacBook Air; but for convenience in having only a single bag on a plane (change of clothes, some toiletries, laptop etc.) whilst also having it be smart enough to use as a laptop bag on its own when I arrive, it seems to be just about spot on. It's also not too heavy at 880g.