If you’re looking to remain in ketosis a little bit of low carb high fat calories isn’t going to break your fast as long as you really aren’t having an excess of 30-40 calories. If you’re going for autophagy then any carbs is going to break that. I would try and maintain a water only fast as long as possible before resorting to coffees, teas, and even apple cider vinegar. I don’t add creamer unless I’m in a eating period. Just make sure you’re getting the nutrients you need during your eating periods because that might be a part of your hunger.
If you’re taking in calories or even using flavoured zero calorie options, then your body is likely releasing insulin, which is an energy storage hormone. Your body cannot burn body fat while being told to store it.