What are some examples of irony in The Grapes of Wrath?

There are many instances of irony in this novel, mostly related to the main theme, man's humanity and inhumanity towards his fellow man. 

In Chapter 13 we see an example of irony when Tom is talking about the burial of Grampa Joad. Grampa has died of natural causes while on the way to California and the Joads have no choice but to bury him alongside the road and move on. Tom suggests leaving a note with his body explaining who he was and how he died because he says that the government is more concerned about dead men than live ones (Chapter 13) and they'll go to a lot of trouble to figure out who murdered him if he happens to get dug up by a work crew on the side of the road. This comment alone is ironic because it demonstrates the government's callous treatment of its living citizens. Tom makes the argument that the government does not care about living men, only dead ones. Instead of spending their plentiful resources to help the living, they spend them on solving the murders of the dead.

Later, in Chapter 26, Ma says, "if you're in trouble or hurt or need—go to the poor people. They're the only ones that'll help." This, again, indicates that the government does not care about the poor. This statement is ironic, however, because the poor are usually the ones needing help, and even though they may have nothing, they are more generous than those who do have the ability to help.

Each of these situations demonstrates the irony of humanity itself in the book. The value that is put on human life is very little, but only by some. Those who you would expect to value human life, like your own government or those with money to help, are often the ones who have the least amount of concern for those in need.