Rabbits can and should have food right up until surgery. Some vets might withhold it for a little bit (maybe 1/2 an hour) so there is no food in the esophagus. Rabbits should also have access to food right when they wake up so the digestive tract can get back to normal as soon as possible.
Ask the vet or other staff if you can bring pellets, hay and veggies for your rabbit. This would be especially important if what you feed is different than what they might have on hand. Familiar foods can help them eat as well. If there is a favourite treat, bring some of that too to see if they can give it to encourage your rabbit to eat.
Have some yummy foods at home for when he comes home. This will help him get back to eating sooner. Veggies are also good to help keep him hydrated, soak them in water and serve wet.