Well, that’s entirely up to you to decide. Water, tea and coffee will also fill you up, same as the other liquids you mention, but it depends on how you feel overall. You can always try different ways too? This may let you know what way you have success with, and what’s more enjoyable. Or you might find as you continue, you might want to change up some, the longer you do it? But being Fat Adapted is a big, major plus, because Fasting is much easier after you are. Can you fast without being FA? Sure. It’s just usually much harder, because the hunger feeling won’t be diminished, and being FA makes it easier.
(For me) I generally only water Fast. (But that was my choice) To be honest, it’s possible the reason I probably do this is because that’s just how I started out. When I researched into LCHF (Keto) as well as Fasting, I did so for many months, and it was said to be the best way to ensure Autophagy. (One of Dr. Fung’s videos I believe) - I also didn’t seem to have a problem doing water only, so I simply kept it that way. But I have fasted before, where I have drank the occasional Tea or even Coffee, I just drink them both plain, or black, with no additives. But nowadays, I do prefer water only, and find it the best for me. … I’ve also seen/read/watched other folks who state there is indeed some things that can be consumed and still get Autophagy? (So it can be confusing, since there isn’t a whole lot of data out there yet, or at least nothing that concrete to say one is better then the any other?) So I guess it all boils down to what you want to try, what works well or what you believe is the best way for you.
As some folks here say, they enjoy fasting more when they do use bone broth, HWC, etc. And there’s nothing wrong with that, especially if it works for them. (That’s what really matters) But I can say that it was Dr. Fung who was one of the folks I watched the most, and that he is said to be one of the foremost authorities when it comes to Fasting. Along with Megan Ramos, who works alongside him. They run the Intensive Dietary Management (IDM Program) and I remember him actually saying on one of his videos that there isn’t enough data on Fasting just yet to provide all the answers. But that it’s his opinion on the water only Fast to ensure Autophagy, but has also mentioned Coffee and Tea should be fine. (If I recall correctly, since it has been a while since I watched those videos)
So I personally don’t Fast for weight loss, since I seem to lose just as much when I’m just eating Keto, mostly OMAD. But it’s more because the way I feel whilst Fasting. So if I do get some Autophagy, that’s just a bonus I guess. 
… But I have read it’s supposed to help with loose skin as well. (from losing all the weight) So if anything, I’d like to hope it may help with this in the long run? For me, I mostly enjoyed switching over to this WOE (Way of Eating) itself and Fasting is just something else I found enjoyable.
Sorry for the long post…
