What are some foods that a dog with kidney failure should eat?

my dog has severe kidney failure and i am looking for some food that would be better for him to eat because it hurts him to eat so he will usually just not eat anything because evidently he has ulcers in his stomach and mouth. i am looking for food, not dog food just regular food from a grocery store, that is low in what ever toxins are poisoning him and that will be more comfortable eat and healthy.