I've been using a plastic box waterer/feeder that attaches to the inside of the cage, but sometimes the tabs break off because some peeps just have to stand on it. It's sort of trapezoidal, and when I turn it over the ice mostly just slides out. I usually get them at the shows, but here is a link in case you want to see one:
https://www.pinnonhatch.com/1.5-Quart-Hanging-Cage-Cup.php
I also use the rubber waterers mentioned above, and those work great, too.
For those marginal freezing days, I put fresh straw in whatever bowl/box waterer they are using. The straw seems to keep the water from freezing so fast and lets the birds break up the ice easier while they are waiting for me to get my boots on.
I also find that if you are using overhead waterers, the drip kind, if you fill them only half way they (mostly) won't break when it freezes. I gather up a bucketful at a time, take them to the house, fill the bucket with hot water, then have a cup of something hot while the waterers thaw. I half-refill them with warm (not too hot!) water and rehang them. I like this because I don't have to open the cage when my fingers are cold.
I do keep some of the 99-cent dog waterers that
Walmart carries, and those are relatively easy to dump the ice out of. (Here's the link:
https://www.walmart.com/ip/4-Pack-World-Pet-Heavyweight-Large-Crock-Bowl-Blue/469419374) However, mice can hang out underneath the winged edges if you don't move the waterer frequently. Any bowl that has flanges on the sides for stability will have that problem. The chickens won't tip it, it won't freeze as fast because of the air layer under the flange, but the mice can move in.
I do have some of the plastic crocks that attach to the side of the cage with a wing-nut, and twist out of the holder, but I don't find those to be easy to thaw.
I also have some real crocks left over from my Dad's rabbit-raising days. I put those in a bucket of hot water, and dump them when the ice releases from the edges. They are heavy and hard to handle when they are cold, but once you warm them up and fill them with hot water, they keep the water warmer longer, and there is no place for mice to hide under them.
Hope this helps!