PRESENTATION OUTLINE
Milk and cereal is a good example for two items that compliment each other, because when you think of eating cereal you think of having milk with it and not water.
Phones and chargers obviously complement each other. When you're buying a phone most times the charger is included/sold to you with the phone.
You can't have a car that runs without gas. Gas and cars compliment each other because you need one in order for the other to have any use.
