Japanese point cards
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.
Speaking of Bic Camera and Sakuraya, if you are a visitor to Japan and buying stuff from these stores, if you show them your short stay visa in your passport, you will be tax exempt - so get 5% off (in cash) and use their point cards to get another 10% off (in points).
If you are a resident here and have your gaijin ("Gaijin" is the Japanese word for "foreigner") friend staying at your house, drag them to the nearest Bic Camera or Sakuraya and force them to show their passport when you want to buy something expensive and you wont have to pay tax on that item. You have to make out that the item is for your friend though. If your friend refuses then just chuck them out of your house.
Back to the point cards. While some of these cards are worth carrying around, most are a load of crap like, "spend 10,000 yen and get 10 yen to spend on anything you want." I cant be bothered with those but my wife loves point cards - these are just some of hers ^^;
When I was living in the UK over 8 years ago, I had a Tesco point card that gave me a penny for every ten pounds I spent. hmmmm. generous.