After living in Japan for a while, you'll notice the amount of reward/point cards that start to build up in your wallet. Some of them are worth carrying around like the Bic Camera and Sakuraya cards. Both of these stores sell electrical goodies and give you up to 19% of the purchase price charged to your point card (its usually 10% tough).
The catch is that you have to spend the points at their store though which is fine by me.