Candy would do the type of work he has been doing on the ranch. He is able to do light janitorial work with one hand and one arm. He could feed the chickens and could probably do most of the cooking for George, Lennie and himself. His most important contribution, of course, would be the money he has saved. This money is the only thing that makes the venture possible for all three men. Frankly, it does not seem like a utopian situation. They would be subsistence farmers and would still have to do some work for others in order to get a little bit of cash for necessities such as shoes, fertilizer, seed, overalls, etc. They would have plenty to eat but very little else. Candy would become more and more of an encumbrance as he grew older. He likes the idea because at least it would give him some security, whereas he has no security on the ranch where he is presently employed. He knows they will fire him if he gets too old or impaired to be useful.
Candy offers to contribute all his savings to help pay for George and Lennie's farm. He also says he can help out with odd jobs around the place:
I ain't much good, but I could cook and tend the chickens and hoe the garden some. (chapter 3)
Candy might not be 'much good', in the sense of being old and decrepit, but he is eager to contribute anything he can to the farm; in fact he is ready to commit his whole life-savings to the project. This shows just how important it is to him, as it is to George and Lennie; and his generous offer helps to make the farm a more realistic prospect. This farm represents an escape for all of them from the aimless, drifting life that they lead. Candy also suffers from extreme loneliness, particularly after his old dog is put down. This makes him even more eager to join Lennie and George's dream.
When, at the end of the story, the hope of the farm is shattered, Candy burst unrestrainedly into tears. This shows how much the loss of the dream hurts him. The final image we get of him is when he is lying prostrate in the hay, as though, like Curley's wife, he were already dead. With the end of the dream, and with the loss of his dog, his old trusty companion, he really has nothing to live for.