Is it true that breackfast is the most important meal of the day? If so, what can I do if I have morning sickness?

You bet. Breakfast is the most important meal of the day. If you have morning sickness because you are pregnant, then see a doctor and you may be able to benefit from vitamin b6 therapy. It is shown to help control nausea in the first trimester of pregnancy. If you are not pregnant, try easing yourself into non-greasy, fruits, cereal breakfast. Slowly your body should be able to adapt :).
Ginger. Agree w previous recommendation. A simple way to reduce nausea is with ginger. You can drink slightly flattened ginger ale or nibble on crystallized ginger. Or pour boiling water over freshly sliced organic ginger & steep x 5 min in a covered pot. Sip. Aromatherapy: sweet orange (citrus sinensis), peitigrain (citrus reticulata), mandarin (citrus reticulata) can reduce sxs.