Post-anaesthesia feeding
Anaesthetics these days are not as problematic as they used to be. Some have a chemical reversal, which means that by the time you collect your pet, the post-op vomiting and grogginess is over, and the animal will probably be able to eat soon after arriving home.
If your pet starts to throw up, remove the food and try again a few hours later. Try offering small amounts of food and water at a time.
Coffee