We don’t think my cat has much time left

I have a beautiful baby boy named Meow. He’s a short haired tuxedo. Twelve years old I believe. He can be a total dick to the other cats, but he’s a sweetheart to humans. Every night he would suckle on my mom’s dressing gown or shirt like a kitten drinking from its momma. He’s been diagnosed with kidney failure. He can’t hold in his urine and a lot of it is mixed with blood. We have a prescription to pick up for him tomorrow and the vets said we need to give him hydration fluid. He’s handsome, cuddly, and honestly insane. It hurts to see him walk so slowly and meow so weakly out of pain instead of his usual chatty meows. It hurts to see him go from jumping up and kissing our fingertips to being so weak it almost looks like he’s not breathing.

I get the really strong feeling we don’t have much time left with him. Any advice for if and when the inevitable happens? Is there anything else we can do to help him and hopefully expand his life span?