yeah, no coconut water. If you really have to, drink some tea (not fruit tea, I mean some green tea or something) if you can't stand the taste of water at all. But really, stick with water if possible.
I have done many 3 days fasts, but I don't think I'm qualified to comment on 21 days fasts.
Start on Friday, hole yourself up in your apartment. Get the food supplies out of your sight and binge watch some movies/series on day 3. Try to sleep most of the time or at least lie down.
I am also an emotional eater. Zen/ vipassana meditation also helps. Every time you get hungry, sit down and try to find the feeling of hunger. Observe it for some time, watch how it goes away. Rinse and repeat.
It's mostly located in your stomach area, unlike true hunger.