I've done 24-hour fasts in the past. I drank plenty of water, some tea, and had some almonds, which help to carry toxins out of the body. You could also do a little rice or bread. Though I don't look it, I am a bit of a glutton. At some point during the fast, I would always have strong cravings for food - I could TASTE it! And not junk food, either, like really good mediterranian or something. It can teach you a lot about yourself, even if you're not religiously inclined. There was usually a heightened awareness that went along with it.
Just recently I fasted for a blood draw; went from dinner the night before through the end of the following work day. The nurse, a woman in her mid twenties, could hardly believe it. She actually asked me if I was insane! I didn't think it was that big of a deal.