A small tin of sardines is a very rich source of vitamin B12, and a rich source of protein, niacin, calcium, selenium, and vitamin D. The sardines also contain vitamins B2, B6, along with others like E and K; and the following additional minerals, magnesium, potassium, iron, zinc, and copper. They are also a source of Iodine and other trace minerals along with being a great source of omega 3s.
Brain food/Power food... if your sardines were cold water wild caught, they were probably all the better. :-)