What symbolic meaning does vegetable soup have in the novel's plot and themes?

The vegetable soup song is Turtle's way of expressing her contentment. She lists the ingredients which are the people that she loves in her life,

"She watched the dark highway and entertained me with her vegetable-soup song, except that now there were people mixed in with the beans and potatoes: Dwayne Ray, Mattie, Esperanza, Lou Ann and all the rest. And me. I was the main ingredient."

This illustrates the main theme of the novel that is a sense of stability, family and belonging.