When fishing on thin ice, or in areas where methane bubbles or springs can create thin areas in the ice, I bring a whitewater throw bag with me. If somebody goes through the ice, I won't want to go anywhere near them, for fear of joining them in the water and doubling the problem. But you can slide or throw a throw bag to a dunked ice fisherman from a long distance away, and use it to pull them up onto the ice and away from the thin ice.
If you make your own throw bag, practice with it so you know how to throw it, and so you know whether the rope will feet smoothly out of the narrow mouth of the milk jug. If the rope gets jammed in the neck of the milk jug when you throw it, you'll need to try a different kind of rope, or you'll need to replace the milk jug with a plastic bottle with a wider mouth.
Try to find a rope which floats, such as polypro rope, for your throw jug.