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.