You can make yours any size. The smallest above (and the example below) is using a piece of fabric 7"x4". If you want to add any fancy machine stitches, do that now. Start by folding it in half as shown, with right sides together. Sew 1/4" seam allowance along 2 sides (see below).
Next, you "box the bottom". See below. Fold each corner so seams match or so seam is at the center of the fold. Stitch across as seen in the picture. This creates a flat bottom like a paper grocery bag or a box. Turn it right side out.
Here is what it should look like from the outside.
Fill the bag with clean rocks and lucky doodads. Top it off with polyfil stuffing or fabric scraps. Run a long hand stitch around the top to gather in the fabric and close up the top. At this time add any ribbons and yarn for hair.
I used felt eyebrows that I hand stitched on at the same time as I attached the vintage buttons for eyes. Now just sit back and let the good luck grow!