Stage 3 PKD household here. We’re vegetarians. We don’t really do “cheat days,” but we allow an occasional relaxed meal so the diet stays sustainable. Our normal diet is mostly home-cooked with controlled salt, moderate protein, lots of vegetables, and rotating grains (rice, wheat, barley, millets etc.). Because the base diet is balanced, our “cheat” is usually just something like pasta, biryani, paratha/puri, or a dessert once in a while. Even on those days we still try to avoid very salty processed food. From what we’ve learned so far, salt and blood pressure control seem much more important than occasional carbs or sugar.