This is a stupid question, but what is the canister on the left? I’ve read it’s a canteen. I’ve been told it’s a gasmask case…
Whoever told you that is…
quite correct Nick. 
It’s a metal ressie case which while it protects the contents very well, can be a pig if you fall over, or lean back, onto it.
No stupid questions here. Its a gas mask canister. Both mask and canister are painted 165 and the little bags are extra lenses.
Stupid? Why would they even carry any of this since gas was never used in WWII?
Although it was of course strictly forbidden many German soldiers got rid of the gas masks and filled the canisters with extra ammo and food.
One of the first thing US soldiers did after D-Day. The bags were pretty useful for stuffing full of extra stuff…I recall a scene from “Battleground” in which the 101st paratroops entering Bastogne during the Bulge and neatly disposed of their masks into a big pile…I still have my mask though. I was given an extra M-17A1 in the reserves and no one seemed to care as they were going to the M40 by then…