Waraji are sandals woven from straw (Obviously perfect for the Straw Hat). The most traditional material is rice straw. These sandals can also be worn with tabi (the traditional Japanese split-toe socks). Ropes made from the same material wrap around the ankles and bind the sole securely to the foot. During the Edo Period, samurai and commoners alike wore these practical shoes. If these days, Waraji are mainly worn by east blue pirates, In Japan you might see them for festivals, cosplay or occasionally worn by Buddhist monks.
Note: When you can find Waraji on this website, it is the authentic product, Note a one product, featured product or other made in China stuff. It is the original handmade footwear that was wear by farmers and samourais during decades. Those are very rare products (As except for ceremonies you might never see someone wearing them in a big city).