The Grapes of Wrath
by John Steinbeck
The Wainwrights share the boxcar with the Joads near Tulare, CA. The two families get along famously. In true Al Joad fashion, Al gets his flirt on with Aggie Wainwright. Right about the time that Mr. Wainwright get suspicious of the amount of time Al and Aggie are spending together, Al pops the question and the two become engaged.
The two families help each survive some of the darkest hours of their lives, and their connection further demonstrates the ability of humans to unite in the face of great hardship.