Well, a sip here and there to allow the food to move a bit smoothly is fine. Better not sip during a meal to quench thirst, though, that may rob you of being able to learn the full feeling.
Also, if you find food does not go down easily, and you need a sip to help along, it may be that you are not chewing well enough. Think carefully why you are doing this, it is best not to make it a habit.
As for the soda thing, it differs with the surgeon, and it differs with the person. Just so that it doesn't go back to an addiction, especially if you had it before.
Medically speaking, it isn't something you can't do without.
Oh, yeah, everything in moderation, so long as you don't forget your protein!!