Your hosts may make adult beverages available at dinner or other times during your cruise. These are included in your paid fare. There is no cash bar onboard. You are more than welcome to bring your own special soft drinks or adult beverages onboard with you and all of the vessels have a passenger icebox
If you have a snack that you just cannot be without you can certainly bring it aboard. Snacks and beverages such as coffee, tea, lemonade, iced tea, and water are generally served throughout the day on board and you’ll likely find that you have more than enough to snack on in between meals.