When the author is short on ideas, this happens. (lol)
It's a single black sock which probably has a value of no greater than 300 yen (depending upon quality level and brand), while two bowls of fruit, and incense, and a picture frame are all being bought to be placed on the altar to commemorate it.
That's going a bit too far... And I say that about the author; not about the onee-san.