I make my bags out of muslin with nylon cord for a draw string. They are about the same material as pillow cases but I make them big enough for elk quarters with bones--two large ones for the hind quarters and two smaller ones for the front--with an extra bag for the backstraps and tenderloins and whatever else comes off. If I bone the meat, I can get by with using only a couple of the bags. These are much lighter to pack in my elk pack than canvas bags. Pillow cases will work fine but if you make them yourself, you can sew them to whatever size you like.
Mike