You should never give dogs milk or any other dairy products.
You should take your dog to the vet. I took my dog to the vets today because he wasn't eating too well either.
The best thing is to take him to the vet. Not eating for a day or two isn't so bad, except you need to know what might be causing this.
Going without water is different. A dog can get very dehydrated if he doesn't drink.
I wouldn't wait, if your dog is refusing to drink anything too. I would take him to the vet as soon as possible.