The Bag pictured above is one my Dad got for me many moons ago, it hangs off my display of camp stoves. It was the inspiration for when I made the canvas cups, a soak-able seal that works exceptionally well. These canvas bags cool via evaporation, and do a pretty damn good job at it. Growing up my Brother and I used those old wool covered plastic canteens, and these cooled pretty good as well. My dad being super frugal, had a wool sock with a handle he could slip a 2L bottle into and soak and hang off the side of the canoe to cool. For those who don't know about evaporation cooling, I found a pretty good description on how it works.
"Evaporation is a cooling process. The water molecules that escape the surface of the bag were those that were fast moving. If you remove the fast moving molecules, the ones left behind are slower and, thereby, colder. The faster you remove them the colder the aggregate becomes. Hanging the bag on the front of a fast moving car is a good way to remove them quickly."
They were typically made of flax canvas, and for the first couple weeks the water would taste horrible as the flax slowly got "washed". One trick was to let the bags sit in a moving stream for a week, then another week soaking in baking soda and water. One the taste was gone, it was gone. while mentioned above that hanging it from your car is a good way to chill it, it also aided in cooling the car in the desert heat. Back in the day one would hang the bags off of the rad cover and place it in front of the rad itself. As the wind blew the water off of the bag to cool it, this water would also blow into the rad and give it a slight cooling effect as well. One of the disastrous things that could have happened while hanging on the car is a drop of gasoline or diesel dripping on the bag, which would in-turn taint the whole bag of water. I love how similar to grain bags of the day the front designs where, classic typography. Canvas Specialty still makes these bags, and can be ordered online. And as you can tell the longer bags were meant to hung on your rad, as it would fill up more area. Also Check the bay and Etsy as there might be a couple on there.