For those who are looking for more space in the same cylindrical format, theres the county comm hydrant, made by maratac. Maratac is much lower quality than maxpedition, it's about on par with condor if not a little lower. You'll find ends of fabric (ready to fray) and lower quality in all components, fabric, strapping and snaps. Mostly the strapping, which feels like a standard poly web vs. maxpeditions higher tensile strength and weather treated strapping. But... It's huge, and it's functional.
http://countycomm.com/hydrant.html
like... huge o_o. Even though it says 16x4, when you take out the insulating sleeve it comes out to closer to 5". It will take (albeit a bit tightly) a 2 liter bottle with a little room to spare on the top.
You get notably more space in the cylinder and in the side pouch, as well as side pals platforms compared to the maxpedition 12x5:
How much extra space? Two extra 230g fuel canisters worth of space.
I don't have a kit set up for it, but I do use it specifically for fuel canister and cooking system storage when hiking. I can strap it to the side of my MR alpha wolf or stow it on the side of my 5 gallon pickle bucket load sling set up (for loading rocks during rock hounding). I ended up keeping the Maratac hydrant over the Maxpedition 12x5 because of the added room for longer hikes (5+days), more storage for random crap, and because it's softer and more pliant when loading larger objects into it. The Maxpeditions zipper and fabric are both really stiff and it makes getting stuff in and out difficult, even though I know it's better quality in every regard. I've been
beating on my Maxpedition lunada set up for well over a year now and it's still stiffer than maratacs stuff when brand new.