chilled watermelon or watermelon rind is something I've seen mentioned often on here as a hot weather treat.
We gave ours a watermelon rind yesterday, it still had a little red meat left on it. Today when I get home I'm sure that all that will be left is the green skin, they eat all the red meat and even the white part of the rind. The rooster would go over between hens and drink the liquid that formed in the depression of the rind while the hens all pecked at the flesh.
I also have some red solo cups filled with saladbar scraps I got from kitchen at work, I fill the cups loosely and put them in the freezer then on a hot day I pop one out into a dog bowl and give it to them. Since it's not packed in the cup they can start pickin at it right away and eat it while still cold.