This week I have an Anime Companion Supplement entry for one of my favorite small things that make visiting Tokyo easier. This is a card that you add value to and use in mass transit and elsewhere. Similar cards such as the Translink system in the San Francisco Bay Area do exist in the US. Rather than go into detail here I refer you to the entry for:
I highly recommend getting one of these cards when visiting the Tokyo area, when your trip is over just keep the card as the value on it is stored for 10 years and you will need it again on future trips.