Currently, canteens can't be filled with anything but a water source from what I understand, but I think it would be neat to give canteens a more expanded usage through the dome, other than water containers. Alcohol, KMB beverages, spiked drinks, I think these should all be able to be carried by canteens, as a way for both Mixers and Corpies to have a portable alcoholic drink to solve alllll their problems.
Something as simple as 'fill canteen with [drink]' that pours the drink into the canteen, and perhaps even the mixing of drinks. One 'drink canteen' consumes one portion of a random beverage inside the canteen, with the canteen holding perhaps up to five portions worth of liquid, or just however much water it originally holds would be perfect.