What did the speaker encounter in chap 13 that made him miss home?

The speaker encounters a cart full of baking yams; the scent reminds him of home. As the narrator is walking across town, he says:

Then far down at the corner I saw an old man warming his hands against the sides of an odd-looking wagon, from which a stovepipe reeled off a thin spiral of smoke that drifted the odor of baking yams slowly to me, bringing a stab of swift nostalgia.

It's a pleasurable memory for him. He says that his family used to bake them in the fireplace at home; they'd take them to school for lunch. When they were at school, they'd eat them happily behind the World Geography book. It was the biggest one there and therefore was the best to hide their illicit snack.
He says that they prepared them in lots of different ways, including roasted with pork and deep-fried in a pocket with dough.
The man selling them calls them hot baked Carolina yams and sells them for ten cents each. When the speaker asks to buy from him, the man asks how many, and the speaker says that if the yam is good, one is enough. It's hot, delicious, and sweet. The seller pours some butter over it for him. As the speaker walks away, he enjoys the flavor and the freedom of walking through the street eating.
Ultimately, he goes back and gets two more yams for twenty cents more.

Despite his various attempts at suppressing his racial identity, the narrator is frequently reminded of who and what he really is. As he's walking along the street one day he's suddenly struck by the delicious scent of baked yams. Yams are a kind of sweet potato that are popular in Africa and the Caribbean. They're also often used in Southern cuisine, and their smell reminds the narrator of his upbringing down South.
The narrator can't resist the delicious smell. So he stops by the street vendor and buys a baked buttered yam. It tastes very good. But more importantly than that, eating the yam makes him feel comfortable in his identity as an African American male. He's not in the least bit self-conscious about eating a baked yam in public, even though he knows it's a racial and cultural stereotype constructed by white society. The narrator is what he is and he doesn't care. Or, as he puts it, "I yam what I am."