The plants are packed to tightly in your containers I would say you have an airflow situation and a blight or bacterial disease is taking over. You container is too shallow. One tomato plant in a container of at least 5 gallons is optimum. Then water the bottom, keep the leaves as dry as possible and as mentioned, fertilize every week or ten days with a low nitrogen fertilizer to replace what has been lost in the watering process.
You location will help a lot, what variety(ies) are in the container, temperatures where you are and how much sunshine. More information is always better.
Now what can you do? Open up the bottom a little, remove the dead leaves and throw away. There is some green left and there may be life left in the plants yet.
