If he isn't eating then there isn't much in there to come out, so since he isn't vomiting, that doesn't concern me too much. It's possible that he has a problem with his teeth or mouth. At his age this is likely. You will want to check your dog’s mouth and look for any broken or discolored teeth, see tartar
on the teeth and possibly red gums
. If you find any, buffered aspirin can be given to a dog with a dosage of up to 5 mg per pound every 12 hours for pain until your dog can be seen by your Vet. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet.
Of course, like Dr. Gabby mentioned there are many reasons why a dog may not eat and drink, so he should be seen by your vet even if it is mouth pain.
He has to keep hydrated and keep his blood sugar levels up, so put a few drops of pancake syrup on his tongue and replace his water with pedialyte or if you don't have any, add a small amount of sugar and salt to the water. Since he hasn't eaten in so long his stomach
is probably upset, so give him some some pepcid. Read about dosages and usage information here: http://www.petplace.com/drug-library/famotidine-pepcid/page1.aspx
Then offer him some small portions of ground up boiled chicken
and rice so he doesn't have to chew it and can basically lap it up. He needs to eat to get some strength up. If you can get some Nutrical from your pet store, you can give him that to keep his strength up until he can be seen by your vet.
I would have him seen now, but if you can tempt him to eat, he should be ok until monday.
I hope this helps.