I've been a huge fan of Premier Protein shakes for the past 3.5 years. Only 1-2 carbs/sugars and to me the best tasting. I've tried nearly every flavor, from your classic chocolate/vanilla/strawberry, to Cookies n Creme; Apple Cinnamon and Oats (which tastes great heated), and one of my favorites Chocolate Peanut Butter. You'd think I had stock in the company! (I don't) but I highly recommend.
Another change of pace is to try bone broth. Swanson makes sipping broths in different flavors which you can just pop in the microwave for a warm and savory (protein) alternative.
Lastly, I discovered this late, sugar-free Popsicles and Gelatin (Jell-o) for both pre and post op (and beyond). Post-op, this will get you some hydration, sooth your insides, and a flavorful treat.
Hope this helps. The first few days are the hardest. You will do just fine!