The Scout Outdoor Essentials, as established by the Boy Scouts of America, are a list of ten items or categories of items that should be brought to any outdoor activity, such as camping or hiking. They are often called by their former (though now unofficial) name, the "Ten Essentials".
As listed in the 14th Edition of the Boy Scout Handbook, they are:
A pocket knife (presumably more than just a knife) can come in handy in a wide variety of situations. It is useful for tasks as large as building an emergency shelter or lighting a campfire with poor fuel, or as small as repairing a damaged backpack.
A first aid kit can be a lifesaver. A basic kit might include adhesive bandages, medical tape, sterile gauze, KT tape, soap, antiseptic, a mouth barrier device for CPR, and scissors.
Extra clothing to match the weather. Multiple layers are superior to a single massive jacket, because layered clothing is adaptable to a wide range of temperatures. No cotton.
Rain gear is very important. Being wet from rain may result in hypothermia, a potentially fatal condition.
A flashlight is, of course, important for finding one's way at night. LED headlamps are preferred to have a red light option for preserving night vision.
Trail food is good for maintaining your energy. However, the human body can reportedly survive for weeks without food, so starving to death should be the least of your worries if you become lost in the wilderness.
Water is probably the most important of the Essentials. Dehydration may develop into heat exhaustion and heatstroke. The human body may only survive for a few days without water. Portable water purifiers and water stills may be used to obtain potable water from virtually any source.
Matches may be used to light fires for heat, or for signalling purposes. (Publicly owned forests in the United States often have lookout stations for forest fires and signal fires.)
Sun protection may include sunblock, sunglasses, lip balm and a wide brimmed hat. Used properly, it will prevent sunburn and possibly heat exhaustion.
Map and compass are probably the most important tools one can carry in case of getting lost, but they won't be of any use to someone who does not know how to use them. In knowledgeable hands, they can be used to determine one's location and the best route to reach another location.