I am not sure that there is anything you can do other than to help keep him comfortable, but let me ask you a few questions:
Does he respond to you?
Has there been recent changes in his appetite, weight, movement?
Has he been urinating more? Drinking more?
When did he last eat?
What color are his gums and inside of his ears?
Does he go outside?
Could he have had access to toxins?
Has there been any vomiting or diarrhea?
Is he able to stand and walk?
Does anything hurt that you can tell?
Are his gums dry?
Any health history?
If you pull the skin up on top of his head does the skin snap right back or does it take a while or just stay there?
I am a bit concerned that your cat may either be diabetic or in renal failure. If he is diabetic then he could very well be suffering from ketoacidosis. With this you may notice a wobbly gait or drunken type movements. The eyes will almost have a haze over them and the pet is usually pretty dehydrated (Gums dry and skin doesn't snap back down when it is pulled up). Symptoms of potential diabetes would be previously overweight cat or currently overweight, increased thirst and urination, decline in appetite, weight loss, and change in personality.
Cats who are in renal failure will drink and urinate excessively, have loss of appetite, weight loss, and vomiting. Their breath will be pretty bad and they will be dehydrated. The loss of appetite is usually gradual rather than acute but can occur acutely if recently stressed, bladder infection is present, or toxins were ingested.
The most you can do for your cat right now is take his temperature to be sure it is around 100.5-102.5F. If not help to keep him warm by warming towels in the dryer, making hot water bottles, or laying him on a blanket that is atop a heating pad set on the lowest setting.
You can also give him water by syringe or dropper every 30 minutes to 2 hours try to get in as much as possible without overloading him and causing him to vomit. Try to offer food but I am not sure he would be willing to take it. You can try foods like tuna, scrambled eggs, even jarred baby meats.
As long as you are getting him into your vet tomorrow I wouldn't worry to much about the food. But definitely try to get liquids into him several times tonight.
Good luck with everything and let me know how things are coming along.