So I took the four patch, lined it with some sheet sewing around the edge 1/8", found some more of the yellow fabric and cut it out the same size as the 4 patch, lined it, sewed em together leaving a small opening, turned it inside out, filled it with ground walnut shells, and then blind stitched the opening and sewed two buttons on in the center. Use a long sturdy needle for the buttons. Sewing the sheet to the pieces first and then sewing them faces together makes it so you are only dealing with the face fabrics when you slip stitch and my guess is walnut shell dust won't be coming through the fabric because it's lined and has to work through two layers.
And as for walnut shells, the prices some people charge is ridiculous. You can get walnut shells, in bags at your local pet store. They sell it for birds and lizard cages. You can get enough to do a gazillion pincushions for about $7.00. Or you can but it on Ebay or Etsy, or your local quilt shop for around $3.00 a cup. My bag had 5 quarts = 20 cups.