I had a pebble with a natural hole in it and it was perfect for a toggle on the bag cord.
The way we play the Story Stone Game is to take turns pulling a stone from the bag, and as each stone is taken out, the story must be continued to include whatever it is you have taken out. My little girl has also been having lots of imaginary fun playing with the stones by herself. Her favourite is the duck. When I get time, and when the snow melts, I have a stash of smooth little pebbles outside somewhere that I can bring in and make some more story stones.