My 3 yr old son is vommiting, and everything he tries to consume comes back. will see a doctor in the morning, what can i give him to eat?

Focus on fluids: Your biggest risk is fluid loss/dehydration. I would find things that the kid will accept as fluids or fluid value & offer them slowly. An electrolyte solution (Pedialyte in US) or 1/2 strength Gatorade can be offered an ounce at a time & let settle. Popsicles, ice chips, applesauce, etc can offer some flavorful alternatives.