The Ten Essentials

The Ten Essentials are the ten items you must carry with you when you hike for your own safety and protection.  The following was borrowed from the Hike Safe website (cited below).

The Ten Essentials

Map
Compass
Warm Clothing
-Sweater or Pile Jacket
-Long Pants (wool or synthetic)
-Hat (wool)
Extra Food and Water
Flashlight or Headlamp
Matches/Firestarters
First Aid Kit/Repair Kit 
Whistle
Rain/Wind Jacket & Pants
Pocket Knife

More specifically, it is important to bring different layers of clothing with you (no cotton!).

Upper Layers

The first layer is a long-sleeved shirt or a T-shirt (no cotton!), depending on the weather.  You should also pack a "windshirt, a lightweight rain shell, and a puffy." (http://goeast.ems.com/gear-to-hike-the-nh-48/)  I always pack a fleece jacket, a rain jacket, and a puffy coat.

Lower Layers

You want to wear/pack long pants or shorts along with rain/snow pants and a base layer (fleece pants, for example).  Socks should be wool (again, no cotton!)

Learn more here: http://www.hikesafe.com/index.php?page=full-gear-list