Transport

We will be in Japan for 48 hours, arriving at Narita and travelling to a hotel near Shinagawa JR station; we have a day there before travelling to Yokohama International Cruise Terminal on day 3.
What is the best travel pass to buy please, from where and will we need cash or card? Thank you

u can buy JR nex round trip ticket =5000 yen

Probably you will have suitcase(s) so you may better take convenient mode of transportation (no transfer, luggage space) so limousine bus or Jr's Narita Express train are your best bet. The tickets for these can be purchased at Narita airport by credit card. Other than that:

You can purchase any JR ticket at their vending machine with your credit card.

Many restaurants, Convenience stores and supermarkets accept credit card but you should ask first if they accept it.

From Shinagawa to the Yokohama port, most convenient will be taking taxi (about 9000-10000 yen/car). You can also take JR train to Yokohama, but there should be no luggage space so you must stand and hold your luggage (this is quite normal for many tourists). From JR Yokohama station you may better take taxi.

By the way we recently visited Sydney and Melbourne and found they are quite tourist friendly. We didin't need to worry about train tickets in Sydney: all we must do was to just tap our credit cards at stations. In Melbourne most tourist attraction was within the free area of tram. You can't expect these kind of friendriness in Japan.

You don't say where you're going so nobody can say if a pass would work for you or not. Or, you can just get a Pasmo or Suica prepaid IC card. As for yen, you can easily use your ATM card at Narita - just go to a 7-11, or 7-Bank ATM, or a Japanese post office.

Frankly for 2 days unless you plan to come back to Japan, I wouldn’t even buy an IC card. Yes, buying paper tickets is a little bit of a hazzel but not so bad either. This is just get a ticket for each of your rides.
I can’t imagine a train pass to pay off. Not even the subway pass because you are at JR Shinagawa so not a metro station.

One problem with the IC cards is that you can't buy them with the credit cards except for the specific card which by itself is hard to obtain.

For only 48 hours you may not want to withdraw cash, so I wrote the way you don't need Japanese yen.

From Shinagawa you can go with JR to Shinjuku, Shibuya, Hamamatsucho (Tokyo tower).

Note that Shinagawa Station serves not only for JR but for Keikyu trains as well which take you to interesting neighborhoods from north to south in Greater Tokyo. Keikyu is as convenient as JR when you're going to the Cruise Terminal (you change trains only once at Yokohama Station where there is less crowd at the very northern tip of the building). Also note that starting tomorrow, Keikyu will accept credit cards when purchasing train tickets of any kind.