I had a cat that lived 24 years on a strict diet of Nine Lives ground chicken and Tuna and a dog that lived 17 years on Pedigree canned so I'm a bit skeptical about all the claims over needing pricey pet food.
My own cat has been eating Purina One Urinary Tract health formula for ages and ages. He had urinary tract trouble when he was about 3 but this food has kept him healthy all this time. He's now in his 17th year and going strong. I give him Wiska's moist poultry in packets as a treat every night before bed and he's happy as a clam. My DH is convinced he's going to live forever... probably not but he sure is trying
For hairballs he gets a dropper of a sugar concoction I bought from the vet whenever I hear him making that hairball noise.