soda card is only for pop. but juice, milk, iced tea, and lemonade are free (don't need the card). if you can live with these options, don't bother with soda card. you can always buy one or two cans ($2 each) if you really want one. I found the free options just fine.
We don't buy the soda cards, we stop at a quickie mart or grocery store and carry a 12 pack (or even 24 pack) onto the ship. Our room steward keeps the garbage can filled with ice and and keep it cold in there - never had a problem with doing this and have been on 8 cruises. You can take it to dinner and they give you a cup of ice. I always pack a drink bottle in my luggage for everyone and we take it pool side with our drinks already filled - we also take it onto shore to avoid any water, drinks from Mexico and the likes - saves us over $100 each trip too.
Your kids will love the soda card. It probably encourages them to drink more soda, but it's worth it. Remember, if you bring soda on board you have to run back to your room when you want one. Godo exercise, but....
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