This is one of the side effects of the stimulant meds. You can keep yourself well hydrated and eat things that are not too challenging to the stomach prior to the med wearing off. It may get better as your body adjusts. If your body does not adjust, you may need to go down in dose (as long as a lower dose like 27 works for you), or add a low dose of a short acting form of methylphenidate just prior to the concerta wearing offm to help ease the rebound.
You and your doctor will need to work at finding the best med, dose and dosing schedule for your needs.
The best thing to do is make breakfast the biggest meal of your day. If you dont have time to cook something, eat a bowl of cereal and drink a carnation breakfast or something similar. Eating a large breakfast will also increase your appitite later in the day.