On Kuro5hin, there’s an amusing tongue-in-cheek essay describing the optimal way to survive a zombie attack. It mostly involves holing up in a mall:
If you took a WalMart like I told you, you don’t need to worry too much about lighting. The skylights do a fair job of illumination during the day, and battery powered flashlights will be OK at night time. But if you’re brave, you can venture outside to get fuel from filling station. And if you’re lucky, you’ll find a tanker truck to drive back to home base. Personally, I’d rather live in the dark. It might be a good idea to keep a CB radio in your car for just this type of event, and try to get a trucker to bring the tanker to your fort when Z-Day arrives.
Near the end of the essay, the author addresses the difficult problem of how long a zombie ‘lives’. This depends on the movie. In 28 Days Later, for example, the zombification is some kind of blood disease. Humans are driven mad, but they still require sustenance. As such, it’s a relatively short-term zombie infestation. In Dawn of the Dead and other zombie films, the creatures are actually reanimated corpses, suggesting that there’s no time line on their shambling existence.
In either case, I think the recommended course of action is to forge a sustainable lifestyle on a previously uninhabited island (or to clear an island of zombies). I’ve never seen a zombie swim or operate a power boat. Regardless of their lifespan, you can live out your remaining years free of fear.