cereal and cheese is a good start. Maybe introduce yogurt to the cheese and crackers, and make sure the cereal has no sugar in it. Gradually add fruit to the cereal. Ensure at least one drink you have during the day is something healthy like orange juice or milk. As for the urge to have a candy bar maybe introduce a granol bar instead. Little 'exposures' to new foods like this will gradually lead to a proper diet. A litte 'win' each day is something to be proud of. Eventually it wil be easier to eat.