A cockle shell is fairly easy to make, and another good pattern to use up any oddments of wool you have left over from other projects. I tried to be fairly realistic with the colours (except for the red which I thought would be Christmassy), but you could go wild and make all sorts. I had an idea that they might look cute with some silver bells, like the nursery rhyme "Mary Mary".
The only technique that might be a bit unusal is making some turns midrow to make the base of the shell thicker. (I have not put in the wrap stitches which I often do, as this didn't seem necessary.) My other tip is not to over fill the shells with wadding, and to a bit of squeezing to adjust the filling, so that the shells are flatter at the edges.) I enjoyed making this striped shell above, which was just done by switching colours occasionally.