This is a great question. Living off the fat of the land is a dream in the novella, Of Mice and Men. The fact that it is a dream reveals the aspirations of the migrant works. At the same time, it shows what they do not have.
Right from the beginning of the story, the men are depicted as alone, alienated, without hope, and without community. Migrant works, usually alone, move from one place to place with no place to call home. They move to survive. In fact, as we examine the men, they do have even have hope for something better. This is why Lennie and George are so different and appealing. Lennie and George have each other and they have a dream to live off the land. When Candy hears of it, he wants to be a part of it. If others heard of it, they would want it as well.
Hence, the idea of living off the land is a dream for Lennie, George, and other such as Candy. This shows what they do not have and what they aspire to have. Tragically, at the end, they get nothing.
Here are the words of the text - Lennie and George's heaven:
“O.K. Someday—we’re gonna get the jack together and we’re gonna have a little house and a couple of acres an’ a cow and some pigs and—" “An’ live off the fatta the lan’,” Lennie shouted. “An’ have rabbits. Go on, George! Tell about what we’re gonna have in the garden and about the rabbits in the cages and about the rain in the winter and the stove, and how thick the cream is on the milk like you can hardly cut it. Tell about that, George.” “Why’n’t you do it yourself? You know all of it."
“No . . . . you tell it. It ain’t the same if I tell it. Go on . . . . George. How I get to tend the rabbits."
“Well,” said George, “we’ll have a big vegetable patch and a rabbit hutch and chickens. And when it rains in the winter, we’ll just say the hell with goin’ to work, and we’ll build up a fire in the stove and set around it an’ listen to the rain comin’ down on the roof—Nuts!” He took out his pocket knife. “I ain’t got time for no more.” He drove his knife through the top of one of the bean cans, sawed out the top and passed the can to Lennie. Then he opened a second can. From his side pocket he brought out two spoons and passed one of them to Lennie.