I got the Wing which mounts between the bottle cage on the back and the seat. The wing comes with a item that can go in one of the sides that can hold two threaded co2 containers. https://www.specialized.com/...s/sitero-wing/105993 Inside my fuelcell i have an inflater valve head, tube, tire leaver, flat multi tool in the main compartment. I have lost a top rubber bit before but specialized sent me a new one after a few calls to rider care the new one fits much more snug than the one that came with the bike but I did put some double sided table in there to make sure it stayed put.

As for the hydration I still use the integrated system. I have used a big bite valve and have not had issues with it. I regularly fill it with water for every training ride now even my shorter 1 hour rides and dont bother with a bottle. To upgrade to two bottles they offer this: https://www.specialized.com/...serve-rack-ii/107003 You apparently can still use the wing from the description as well.