Prepare for Radiation
Far Harbor has a lot of radiation. Yeah, you may be thinking “all of Fallout 4 does, the game literally takes place in a nuclear wasteland.” And while that is true, Far Harbor kicks it up a notch. Like, a really large notch.
There are plenty of areas that are just drowning in radiation. In some spots it gets so bad that just going in with your normal armor will guarantee your death. Like all things in Fallout 4, you do have ways to prevent an untimely demise in the face of nuclear threats.
You don’t want to over-rely on RadAway, though. It’s much better to avoid the damage altogether. Bring some good, rad-resistant gear to keep your health reserves up. Power Armor, Hazmat Suits, whatever you got. Make sure you keep something in your suitcase to throw on whenever you hear that Geiger counter start ticking.