something called a “slush mug.” I guess you probably could also have called it a “water ice mug.”
The slush mug had some kind of liquid contained within its walls, and you would keep it in the freezer. Then, whenever you were in the mood for slush, you would take your pre-frozen slush mug out of the freezer, pour in your favorite chilled liquid…juice, lemonade, root-beer, or whatever…and start stirring. In a few minutes, it would make an instant mug of slush.
Actually, I had two of them. Unfortunately, that was one of the few things that I’ve thrown away in the last few years, when I found them in the back of the freezer and realized I hadn’t used them in years. I wish I could have sent them on to you. I wonder if you could find something like that anywhere these days? It made it easy and fun to try different kinds of slush.