The usual ingredients are N-P-K which is nitrogen-phosphorous-potassium and the amount of potassium is higher because it is needed for flowering and fruiting.
Magnesium, seaweed extract and wetting agents may also be found in tomato food.
Magnesium is needed by the fruit and enhances the flavour, seaweed extract is an organic stimulant and contributes to the general health of plants and a wetting agent helps the distribution of moisture throughout the entire root area. The wetting agent is useful because it helps prevent blossom end rot ... a problem caused by a lack of calcium.
Not all tomato food contains trace elements because most of these elements are needed in small amounts and can already be found in the compost/soil.
My own personal view on this is that if your tomato food does not contain trace elements, it is a good idea to give them a feed with a food that does during the period when they need the energy most which is when they begin to fruit.
Food containing trace elements could be given once a fortnight during the summer period but remember that "little and often" is always the best way to feed tomato plants.