Yeah so this is confusing, but filling your canteen refers to how guys would try and make out with as many girls as they could before leaving on their Mormon sales trips (missions). The idea is that you would have girls to think about while you were forbidden to hardly look at them for 2 years unless it had to do with selling the Mormon religion. It’s very toxic and usually the girls would carry the brunt of this because the boys were justified in breaking up because god had a mission for them.
