I originally purchased a 45L Patagonia Black hole duffel as I needed something lightweight and soft for my trip to Africa, where it would have to be squished the cargo bay of a small Cessna (we had a strict 33lb limit for all bags, including camera gear so I thought the GR2 was a bit too heavy and rugged). The Black Hole duffels are affordable and versatile enough to be worn like a backpack and crumpled down to a tiny size when not in use (they fold neatly inside themselves).
I found myself using the duffel on other trips afterwards and ended up adding a larger 60L model as well. I still use them as carry-ons.
Lightweight, weather-resistant, folds flat. I have this in both 45L and 60L sizes. Great as an extra bag for bulky things when traveling. It seems like they have since updated them so there's a 55L model instead of the 60L.
