Dan's helpful injury
Although Dan probably wouldn't prefer his serious injuries, obtained while working on a ladder, his case is helpful to the union interests because it shows precisely what the labor union would provide. Dan is injured on the job and is denied medical attention, which is simply cruel, and beyond that, there is no worker's compensation or paid leave. He is suddenly unable to work, and his employer feels no onus to provide for him even though the injury happened on his property while working. The union takes them to task on this.
The symbolic irony of apples
Doc manages to find a place where the "Fruit Tramps" can meet—an apple orchard where they can eat apples for free. The scene is ironic in two ways at least. First of all, they are meeting to do something good, but eating apples in an orchard they don't own is a strangely suggestive metaphor, since the imagery belongs to the fall of man sequence (which Steinbeck of all author's knows—after all, he wrote East of Eden). Secondly, they are depending on a farmer's generosity while organizing against other land owners.
Violence in the garden
When Sam is forced to chase men away, the scene turns into pandemonium. Violence is seen as an ironic problem, because Jim gets shot, and several more are put in serious danger, because although their motives might have been the best, the execution was reckless and tactless, because they were emotional and violent. Ironically, they are liable to destroy themselves in their passions.
Dakin's performance
When Dakin is confronted by the police, he acts like a crazy person. Yes, he was flustered from being attacked an overwhelmed, but he only achieved two ironic outcomes: he lost his chance at restitution and he made the party look bad in the eyes of law enforcement, which puts a serious damper on their spirits and severely undermines their odds at success. He does the opposite of what a leader in his position should do, because that could have been an opportunity to earn police support.
Joy's death
The death of Joy is a symbolic event (the words themselves are suggestive enough), but it is also deeply ironic. The death of Joy at the hand of scabs means that the movement can catch a second wind. It is a troubling way to make progress, but it also indicates the stakes of their movement. They deserve to be treated as humans, because just like landowners or policemen, the working class also only has one life to live, and that life is as valuable as any. The death is an ironic source of power in the movement, making Joy into a martyr.
