The healthiest people I know have all ignored the dietary advice and eaten a varied diet.
Water is good, but the 8 glasses a day is humbug. Many foods contain water in them. Just drink when you're thirsty. If drinking water displaces soda or juice, that is probably a good thing.
If you are feeling a yearning for a particular food it is probably your body telling you that you need something in that food. There might be a substitute available if you know what precisely your body needs, but don't ignore it.
Some evidence hints that certain sugar substitutes mess with the gut bacteria and indirectly cause weight gain.