Here are a few:
1. "the fireplace commenced its seasonal roar" (this could also be an example of personification, but only if it is the roar of a person - I see it as the roar of an animal, perhaps a huge bear, and thus metaphor)
2. describing a hat, "a straw cartwheel corsaged with velvet roses"
3. Dusk turns the window into a mirror
Remember that a metaphor is a comparison without using the words "like" or "as" (which would be a simile), so look for things that create a picture in your mind of something else, as in the case of the window. It is not a mirror, but at dusk, it looks like a mirror. Writing "dusk turns the window into a mirror" however, is a much more beautiful way of making the comparison.
Metaphors are not present in literature merely as brief descriptions but as overarching thematic elements as well. In this way, metaphors can help widen understanding and deepen the impact of a story. Certainly this story has many brief descriptive metaphors, such as "Dollar bills, tightly rolled and green as May buds" and such descriptions can also hint at larger themes. Capote's writing is so skillful that even one brief phrase can serve to illuminate the entire story. In this example, the "May buds" represented by the dollar bills are reminiscent of hope, youth and the seemingly-eternal cycle of seasons, and all three of these are themes that inform the entire story.
Hope: Buddy knows that poverty defines his existence but he relishes the optimism and resilience of his elderly relative; the image of the bills as May buds suggests he knows that better times lie ahead.
Youth: Buddy's age during the majority of this memoir is belied by the very adult ways in which he describes this memory, but it is from the vantage point of adulthood that he can more effectively communicate the emotions he felt as child during these Christmas activities.
Cycle of Seasons: the repetition of the cry of "Oh, it's fruitcake weather"and the description of the seasonal activities (picking pecans to make the fruitcake, buying the whiskey, gathering greenery for decorations) serve to anchor this particular episode within the context of a number of years where the same events took place again and again, creating a rich and enduring memory for the author to draw upon.
Even though Capote later became a rich man after the sale of his book In Cold Blood, he clearly valued the wealth of experiences he had as a child living in relative poverty, thanks to the loving woman he lived with.
Describing a hat, "a straw cartwheel corsaged with velvet roses"
Metaphors are all around us in everyday speech; when someone says, "You're a rockstar," for example, it's a metaphor—because, sadly, you're not really a rockstar. It's just a more interesting way to say, "You're great!" So a metaphor is just one type of what you've probably always called a figure of speech, like when you call someone who's really boring a "stick in the mud" or a "wet blanket."
A metaphor is a tricky balancing act: if it's too similar to what you're describing, it won't be interesting. If it's too different from what you're describing, it won't make any sense.
It's also hard for a writer to come up with new and original metaphors; when everyone's already heard them a million times, they become uninteresting and what we call cliché—like all of the examples above! That's why Truman Capote's metaphors are so interesting. They fit their situations perfectly, and he made them up based on the way he saw the world.
Let's think about the elderly woman's "cartwheel" hat early in the story. It seems like a metaphor to us—a big, round hat like a cart's wheel—but in the 1950's, cartwheel was a common name for that particular type of hat. So to Truman Capote it wasn't really a metaphor. But, then, think about this: way back when those hats first came into style, their name began as a metaphor, because that's what those hats reminded somebody of! Language is always changing!
Have fun looking for metaphors! They're everywhere! And don't get confused if you see some metaphor-like figures of speech that have the words like or as in them. They're called similes—like the word similar—and they compare two things, using like or as. So instead of saying you are a rockstar, a simile would say you are like a rockstar.
Here are some examples of metaphors, the definition of which is stated above in the previous answer.
"A person my age shouldn't squander their eyes"
Obviously, a person cannot truly squander their eyes as one would squander money, but in this case Buddy's friend chooses to look through her eyes at other, more wholesome, things.
"The cost of stamps turned our purse inside out."
While a cost cannot literally reverse the wall of a purse, the cost of the stamps caused the buyer to spend all their money.
"A brief rope of dilapidated, undoubtedly dangerous candy like light bulbs"
In this case, the string of brightly colored Christmas lights is being compared to equally brightly colored sweets.
"We scrape together a nickel."
Again, the speaker is not physically scraping the floor for money but is just able to make enough money to equal a nickel.
"Plunging through the healthy waist-high grass"
And finally, a person can't truly plunge into grass as they would a liquid surface like water, but in this case they are "swimming" is a sea of grass.