If he's going to the vets tomorrow the best you can do for him tonight is to try to get him to eat something. Great advice on the humidifier. Even better is if you could take him into a small bathroom and turn on the shower hot to steam up the room. That may open his air passages enough to let him breathe. Stay in the bathroom with him of course. Let the room steam up and stay in for a few minutes. See if it helps any. You can wrap him in a blanket or towel to keep him from catching a further chill.
If he isn't eating the food you put in for him it's probably because he doesn't recognize it as food. It sounds like it's hard food, not canned? He looks like he is around two months. Cute little gaffer. If you don't have canned food available then the best you can do is tuna, sardines or salmon. The raw chicken may do the trick too.
Does you have any L-lysine there? If you do try to add a small amount (1/4 tsp) to whatever food you get him to eat.
What are the chances he's feral? With the ear mites and possible fleas (scratching in the one pic) I think he possibly could be. Thanks for stopping for him.