You can purchase the "soda card" in any of the bars. If you want it, get it the first day to get the most of your money. It runs somewhere between $40 and $45 for a 7 day cruise, unless they've recently changed the prices.
They apply a sticker to your room card indicating that you are participating, and then you can show your card in any of the bars or restaurants and get a soda. It won't apply for cans of soda, unless you find a friendly bartender, but just the fountain variety.
A can of coke costs $1.75, plus a 15% gratuity, so you'll need to figure out if you drink enough pop to make it a wise buy. For my DH, it's a definite yes -- for me, it's a maybe.
Our first two NCL cruises it included an insulated coke cup, which held no more than 12 ounces, but on our last cruise that was an additional $2. We don't usually worry about the cups -- for us, they're more trouble than they're worth.
Have a great time on the Jewel and let us know what you think. We're sailing her for the first time in November! By the way, your English is fine -- certainly much better than I'd be doing writing in a different language.
I don't remember all the kinds for sure. NCL carries coke products, and I know for positive they had coke, diet coke, and sprite. My daughter also got a ginger ale one night -- in hopes the the ginger would help her mildly upset stomach. They don't have diet Dr. Pepper -- which is my drink of choice -- so I usually buy a twelve pack and take on to have throughout the week.
As far as water, I'm pretty sure it doesn't apply to bottled water. I like the tap water on the ship just fine, however, and actually drink more water on the ship than I do at home. They will have bottles of water you can buy, but I think they were more money than I was willing to spend. We actually carried on our own water last year too, along with the Diet Dr. Pepper, so that we'd have plenty for excursions.