I was just watching
An Ache in Every Stake, and the scene with Curly shaving the ice made me wonder again what they used for the fake ice blocks. I don't think they had Styrofoam back then, so what the heck did they make them from? Does anyone know?
(I also noticed that when the Stooges arrive at the base of that long stairway and Moe cuts a piece of ice for Curly to take up, he chops it with the axe and you can see splinters of real ice fly out onto the tail of the truck, but they aren't there when the camera shifts to show Moe giving Curly the "ice", and there is only fake ice blocks visible in the truck.)
Update: according to
Wikipedia, Styrofoam was invented in 1941, so I suppose it's
possible that they used Styrofoam.