Without the conveniences of home, basic tasks require some preparation. I found this resource for how to boil water without a kettle in “The Book of Camping and Woodcraft: A Guidebook for those who Travel in the Wilderness,” by Horace Kephart, 1906.
How to boil water without a kettle
In my chapters on Camp Cookery are described many processes for cooking without utensils; but, it may be asked, how could one boil water without a kettle? There are two ways of doing this. One of them, which many have heard of, but few have seen, is to split a log, chop out of it a trough, pour water in, heat a number of stones red hot, pick them up, one at a time, with a forked stick (or with one beathed in the fire, at its middle, and bent into hairpin shape), and drop them one by one into the water. To do this successfully, one must choose such stones as will neither burst in the fire nor shiver to pieces when dropped in the water.
Another way, which will be news to many, is to boil the water in a bucket made of birch bark, heated by direct action of the fire. The only difficulty about this is in so fastening the sheet of bark, below the waterline, that it will not leak.
Take a thin sheet of birch bark, free from knots or “eyes,” and make a trough-shaped bucket, as illustrated. Pin the folds with green twigs below the waterline. Pour the water in, set the bucket on a bed of fresh coals that do not flame, pile coals around it up almost to the waterline, and let it hum.
It might seem impossible to melt snow in such a bark utensil, but the thing can be done when you know how. Place the bucket in the snow before the fire, so it will not warp from the heat. In front of it set a number of little forked sticks, slanting backward over the bucket, and on each fork place a snowball. Thus let the snowballs melt into the bucket until the vessel is filled above the pins that hold it together. Then set the bucket on the coals, and the water will boil in a few moments.