Because of the climate and the land here, we frequently hike where it is muddy. Or swampy. Or snowy. Or marshy. But mostly muddy. Gaiters cover the tops of your boots/shoes and the lower parts of your pants tuck into them.
Gaiters keep the hems of your pants from getting wet and/or muddy, keep falling water out of your boots, and --for me-- help my boots stay tied. Also, they're additional protection from ticks, which are getting really bad on the east coast.
These are my favorite gaiters, and unless it's been dry for a week or two, I put them on automatically before going into the woods.
I treat all our hiking clothes with Permethrin spray. Pants, shirts, hats, shoes--everything gets sprayed. The treatment lasts through six washings.
I have curly wild hair. That means I rarely leave the house without a hat, and always grab a hat before I head into the woods. My favorite sun hat is by Outdoor Research and has a wide brim to protect me from the sun. It's UPF 50 and can be thrown into the washing machine when it gets sweaty. It's perfect. I also have winter hats--the main criteria there is to keep my ears covered.
Although we both have cell phones, we have a handheld Oregon GPS and Garmin Nuvi for the car. The handheld because I like keeping track of where we've been, and the software allows me to geo-tag my pictures. The Nuvi because a lot of places in WV don't have cell signal (there's nothing like wildly guessing which way to go home when you're in an unfamiliar place). I also recommend an Atlas and a Gazetter, because often the best places to hike are going to be away from civilization and it's good to have alternate ways of figuring out where you are.
As a note, we set the car GPS to always have north at the top, and zoomed out. That makes it easier for me to switch from map to GPS and has greatly helped my sense of direction.