Although I love to cook, and I am always experimenting, I have yet run into a situation where I need tomato juice. However, friends tell me the horror story of making a recipe that causes for tomato juice only to find out in the middle of adding the ingredients they have none. So, I have been told if you run out of tomato juice and you need a quick substitution. Quickly mix ½ cup of Ketchup with ½ c of Water. That should hold you over.