What are the two elements of the backpack/rucksack on the Napoleonic Russian infantry in greatcoat and what colour are they? 

HI they are backpack (black) and canteen (silver) hope this helps BUSTED.

Exactly - Backpack and canteen.   It's what all the illustrations show.  Speaking personally, and from hard earned experience, putting something squashable strapped to the outside of a pack is asking for it to be flattened and lost very quickly...
 

Thanks both.