Sodas/tea/coffee/cocoa/milk/and juice (in some locations) are free in the main dining rooms, buffet areas, and deck 9 beverage station. If you want a soda at a bar, you'll be paying for it.
There are daily mixed drink specials that cost less on those days. It would be listed in the Personal navigator or navigator's app. There are also free drinks at things like the officers/captain's reception on formal night, and some of the Disney vacation club events (champagne and mimosas).
Yes, the only thing we paid extra for were alcoholic drinks and the 'specialty' non-alcoholic ones at dinner. (and tips to the Room Service person)
In addition to all the 'quick service' places on deck 9, you can get free snacks at Cove Café (the coffee costs extra there...but we just got the free coffee at the beverage station and then went to get the free snacks), free soft serve ice cream up on deck 9, and there are some free snacks in the evenings in the pub and promenade lounge--but they're out pretty late--say 10:30-11:30PM.
On a 7 nt cruise, you can sign up for the free character breakfast, it was held in Animator's Palate for us.
As far as photos--a Disney crew member can take pictures of you with your camera. (The Shutters people won't.) I just stayed FAR away from Shutters and never even looked at our pictures so I wouldn't be tempted. I knew we had enough of our own good pics and the package was just so pricy--much more than the packages at Disney World.
Enjoy your cruise! We loved the Alaskan cruise!