I've never been on Holland America, but I've taken several cruises. Each one had a similar policy about sodas. Depending on the cruise line, you can purchase a refillable glass or a a sticker that is placed on you key-pass Each time you want a soda, you present the glass or show the sticker on your key-pass. I think some lines has something equivalent for alcoholic beverages, but I don't drink alcohol so I'm not sure about that.
Coffee (except specilaty coffees), tea, milk and juices are free all the time and available all the time, whether you go to a dining room, buffet venue or call room service. Some cruise lines even have a supply of tea and instant coffee with sugar and powder creamers in your stateroom,and that supply is refereshed daily. There may be a charge for certain juices at dinner - ask your waiter or barperson when you order.
Remember, that for each beverage you purchase (including alcohol, specialty coffees and sodas) you will have to pay a service charge. The service charge may vary from cruise line to cruise line, and since I don't drink much of any of those, I couldn't tell you exactly what the service charge is. On the lat cruise I took, service charges (ie tips) were charged at 18%.