When I was a little girl fruit was limited to what was in season - so it was a big treat to get an orange in our stocking. Now living in Southern California my daughters thought it was a very odd custom, but it was normal for my friends and I living in the Pacific Northwest. It is my understanding it was something my parents received too.
We also kept a bowl of mixed nuts to crack from Thanksgiving to Christmas.
My parents are gone now and so I cannot ask them why - it was just something we did and everyone i knew did it too.