Hi ironraven,
My packs are 32 L (Osprey Stratos) and 40 L (Osprey Switch). The Switch doesn't have side bottle pockets and the Stratos ones are designed in a way that, if you put standard Nalgenes in there, you lose some loading capacity *inside* the pack (the bottles kinda push into the pack).
A while ago, I went from carrying Nalgenes over to a Source 3 liter hydration system like this one :
This works perfectly in both of my Osprey packs, I love it! My Switch pack even features a neat insulated hydration tube sleeve. In the end, I always carry 2 or 3 liters of fresh water in my pack and stopped carrying Nalgenes. If I need extra water, I will pack a 2 L Platypus collapsible bottle.
The idea of putting my PSK is a metal container seems to make the most sense in my case. Do you have an idea where I could find a rectangular, box-like soup can? ;-)