Traditional waraji sandals are made from woven straw. They are constructed on a loom and are a little smaller than the foot they're made for, ending just behind the toes. The toes hang out over the end of the sandal. Along the sides of the sandal are four small loops (two on each side) and four strips of woven rope come through the forward end and back end of the sandal. These are threaded through the loops and wrap around the foot and ankle to tie them in place.
When you do a search on ebay or different "cosplay stores" for Bleach cosplay items, you'll usually find these sandals sold along with a set of tabi socks. These sandals are more traditional but have several problems that don't make them ideal for cosplaying.
First of all, they don't look very accurate to the manga or show, and if you're like me, accuracy counts on a costume as "simple" as this. I don't mean simple to construct, but the fewer details a costume has, the more crucial it is to get those details right.
These sandals also don't hold together well. I had ordered a set, and put them on a few days before the con while making the costume to get used to the way they felt. After wearing the sandals for a little over two hours on concrete, linoleum, and carpet, they completely fell apart. Other cosplay friends that have ordered these sandals have had the same problem and you see this happen at cons all the time - I've never seen anyone wear the same set for more than one day without them being severely degraded, fraying, or falling apart.
Shinigami sandals as shown in the manga and anime differ from traditional sandals in two ways. Shinigami sandals extend all the way to the end of the toes much like a normal sandal. The sandal itself also extends past the heel to wrap up around it and end at the Achilles tendon. It's a very subtle effect but one of the most distinctive characteristics of the outfit. I've never seen sandals online that you can buy like this, so I decided to make my own.
These sandals take a few hours to make. The first pair costs about $15, while subsequent pairs can be made for a third of the cost. You can size them to your specific foot, which is also comfortable. Best of all, you can wear these sandals to a con for three days of walking for 10 hours each on concrete and asphalt before they break down.
All in all, definitely worth the time invested and always turn heads. I've never worn these without people rushing to comment on them and asking how they can make their own!