I am sorry to hear you are worried about your cat. My name is Rebecca. I am a veterinarian and will do my best to help.
How long has he been unable to keep food down?
How old is he?
Is he able to drink, and keep water down?
There are many reasons, dozens of them, why cats vomit like this. It can be from an obstruction in the stomach or intestines, so that food can't pass and has to be vomited back up. It can also be from liver disease, pancreatitis, kidney disease, cancer, even heart disease makes cats vomit.
The best place to start is with a good physical examination: palpating lymph nodes and internal organs, listening with a stethoscope, checking for dehydration. If he can't hold anything down, he may be dehydrated and that his condition worse, and he needs supplemental fluids.
Until you can have him checked out, try to keep him hydrated by offering water, broth, or tuna juice. If he won't drink, or can't hold liquids down, he really needs medical attention. You can try Pepcid AC (famotidine) 1/4th of a 10 mg pill for vomiting.
Let me know what else I can answer.