In "A Christmas Memory," what is different about this particular Christmas in Buddy's memory?
This story recounts many detailed memories of Christmases Buddy spent with his elderly cousin Sook, and though he is describing one particular Christmas he often mentions that their activities are things they have done in years past. We learn near the end that this is their "last Christmas together." This fact imbues the details of the story with more intensity, and perhaps explains why Buddy/Capote felt the need to tell the story. There are also hints that this particular Christmas contained some occurrences that had not happened before; for example, there is a bit of whiskey left in the bottle after the fruitcakes are done, and they both drink it. This causes Buddy's other family members to scream at his cousin for endangering a child and also for the immoral act of drinking whiskey (they are quite religious). Buddy tries to comfort Sook's hurt feelings, telling her she is too old to cry, to which she replies, "I am too old; old and funny."
We learn this is the last Christmas they have together, and as Buddy says, "life separates us." He says he goes off to military school and hears secondhand that his cousin continues to grow frail and eventually dies. This gives deeper meaning to Sook's words while they are flying kites, that she could die that day—"I could leave the world with today in my eyes"—having enjoyed the beautiful windy day and kite-flying with Buddy.