This is the one!  These Osprey Porter 46L backbacks held all of our gear for 1 year around the world. They lasted through airports, ferries, trains, and even the back of a motorbike.  The two key elements that made me feel like a organized and sane person (instead of a "filthy backpacker") were the fact that

1. The bag had a computer organization area

2. The bag zipped all the way open

That made all the difference in the world!