OK, so were you actually expecting the literal answer to the song, ’cause that gets pretty monotonous pretty fast. Just in case, one more time, “A partridge in a pear tree” (or an alternate version, “A Fire Breathing Dragon Just for Me.”)
However, my initial thought was that we’d be creating a list of our own 12 days. In that case, my answer would be “A bright and shiny iPad on my knee.”
Maybe you can clarify the intent.