I thinking about getting a cheap bottle carrier for my GSI bottle/cup for when Patty and I just go over to Mingo again and need a little water. When we can walk around again she could carry it. And I'll still have my 511 bag with another bottle/cup sit up in it.
The Maxped bottle holder I have, can easily be turned into a shoulder bag. It has clips on it just for that. Horn Dog has a setup made with one. However, even thought my Nalgene and Spacesaver Cup fit into it, it is a PITA to get the cup out. It goes in smoothly, but isn't fun to get out. That is why I put the Nalgene bottle in first and then put the cup on the top of the bottle before zipping it up.
If you get the biggest Maxped bottle holder, this wouldn't be an issue and you could even put a little solid fuel stove in with it with a freeze dried meal in the side compartment. It would be like a compact little 12 hour sustainment kit.