I did post on your other thread about the bar, but maybe I didn't make it clear. Most people just run a tab for the length of the trip. It's much easier all around. As I said, everything you purchase on the trip gets charged to your cabin, and you get a statement the day before the end to check before they actually run the charge. That's with the exception of the gift shop, which is a contract operation. And they take credit cards. There are display cases near the reception desk that have things like fleece jackets and vests, embroidered aprons, etc. Those are not from the gift shop and if you get any of that, it's charged to your cabin.
There are several photographers on board, who also serve other functions like entertainment, and they post the prints of the pictures they have taken each day near the restaurant. If you buy any, they have to be paid for to the photographers in rubles.
I had a wonderful time on that trip, and I'm sure you will too.