We've previously used a shower curtain liner to keep picnic blankets from getting soaked by wet grass, and we've sewn rock pockets to make sure it doesn't blow away. Complete your picnic blanket trifecta by sewing a tote that keeps your blanket organised and gives you a convenient handle.
Full instructions can be found on craft blogger Cherry Menlove's site at the link below. Essentially, you're measuring the circumference of your rolled-up picnic blanket and cutting out two pieces of fabric that are a little over that length to give you room for your closure. Sew buttonholes and attach buttons on the opposite ends of the tote, and then cut and sew a handle out of the same material. Cherry uses the same fabric for the tote that she did for the underside of the blanket.
How to Make a Picnic Blanket [Cherry Menlove]