Tourist Tip #1: Invest in a Suica or Pasmo IC Card
The Suica and Pasmo IC cards are e-money cards that can be used in a variety of ways. The two most practical: riding public transportation and shopping. The cards are accepted at an impressive number of locations, including convenience stores, coffee shops, coin lockers, vending machines, and many department stores.
The difference between the two is simply one is sponsored by JR (Japan Rail), the other by cooperating non-JR train and subway lines. While you must buy the correct card depending on which train line you take, they are essentially interchangeable otherwise (you can use either for both lines and can charge either at both machines).
The cards are easy to obtain, you can purchase either one from any train station. Fitting easily in your wallet, having one (or both) eliminates the need and worry of carrying cash around, as well as fiddling with money you might not yet have gotten used to. Both cards can accept sums well-over ¥10,000, although only require a minimum ¥1000 deposit - and are an integral part of the lives of people who live in Japan.
Information regarding the cards (in English):