My gastric surgeon told me newer research has shown coffee is an appetite stimulant and for that reason should be avoided if possible, but he conceded a single cup now and again should be okay.
I was never on a liquid pre- surgery diet, just a no carb/low fat diet 10 days pre-op and I still had a slice of pizza in the middle. A liquid diet x2 weeks is old school, don’t beat yourself up too much pre-surgery if u are on it....