My 11 year old shepard for the past two days has barely eaten anytbing and has thrown up. His behavior has changed to where he rarely gets up.He is drinking so much water though. The vet and animal hospitals are closed because its Sunday. Any advice or any thing I could do to get some food in him until tomorrow? Please help. Im so worried and desperate for answers.

You need to find an emergency vet in your area. Feeding a vomiting dog will result in nothing but more vomiting.

In an 11 year old large dog, it could be so many different things, and you need to be prepared for something serious. Have you felt all around his throat and belly, and looked at the color of his gums?
My 11 year old golden had similar symptoms and had lung cancer. The vet gave me prednisone and sent us home for as many days as I wanted to spend with my dear dog before bringing him back. I'm not saying your dog has cancer at all! Just to be prepared because of age.