How to open and what to make with the shell
Prise open carefully with a knife and scrap out the nut pieces 
stick down onto card with a strong glue, eg uhu into a clover shape with the points on the outside 
when dry cut around shape of nuts or make a circle and decorate with maybe glitter -a natural candle holder. A perfect present with a matchbox house and a candle –see other posts 
Can fill the walnut with a little surprise eg ballon, coin ,sweet 
Hold shell together with two pieces of blue tac or tie a ribbon around , can even hang on a Christmas tree or can make twelve for the days of Christmas !