Black coffee is good for energy. A lick of salt helps me when I have hunger. Good luck to you! Get lots of rest. The first days are the hardest, then it gets easier. Have a plan when you will break the fast to take in proper low fiber food/soups. Drink lots of water during and after.
Some say a true fast is only water, salt, potassium, and magnesium. Others say you can do calorie-free stuff like black coffee, teas, or pickle juice. It all depends on how hardcore you want to go, really. I like to do just water so I give my body a chance to cleanse from everything. Whatever you do, though, stay away from chemical sweeteners (zero calorie) and other unnatural additives.
How long are you going for this first time?
Set yourself up for an easy transition by eating low carb the day or two before you start. Otherwise the hunger pangs tend to be worse.
When you start feeling hungry, drink a bunch of water. I also start training my brain that those pains are GOOD. “Yes! That’s a sign my body is getting a chance to heal and get into ketosis and autophagy. Keep rumbling, belly! You’re doing great!” Just start associating those sensations with the good it’s doing inside your body.
If you want some really inspiring (but hardcore!) tough love, check out the Snake Diet videos on YouTube. They ALWAYS do a great job of motivating me to stay on track, and they’re hilarious because Cole is so nuts. But he knows what he’s talking about!
Oh! And look at joining the Reddit Rolling 72s group (or circle, they call it) on the Life fasting app. That app is my fave because it shows you what’s happening in your body at different stages of your fast. Bonus motivation!