So let's say you have a condo in the Keys or you're motoring the Winnebago to Phoenix for a month or so. One of the first things that should occur to you is that you're going to be in a different state. That should set off an alarm that you're going to places with different local laws about things like health care directives. In fact, nearly all 50 states have their unique takes on what goes into those documents, what can be done with them, and how they must be executed. Still, if presented with New Hampshire's version, doctors and hospitals in most other jurisdictions will honor it as much as possible - "full faith and credit" is what the Founders called it.
What that means is if you're going to be somewhere out of New Hampshire for more than a hopeful weekend at Foxwoods, it's a good idea to take a copy of your Granite State directive with you. If you have a car accident on the Tamiami Trail or your heart starts palpitating on the rim of the Grand Canyon, your agent - probably your traveling companion - will have the necessary authority in hand to make sure you get the emergency help you may need. And lest there be any doubt, a spouse doesn't have the right to make health care decisions for you just by virtue of that relationship; you need the official designating document.
This also suggests that if you're spending a lot of time somewhere else, it may be worth tracking down one of the local directives or proxies or whatever they call them there. You may not even need a lawyer, because many states' forms are available online these days. Even many hospitals have them printed up with blanks to fill in - MCH does. Then once you've got them executed, you'll be stress-free, as well as warmer than the rest of us. Travel safely.