A cell phone, provided that you are able to find service, is the easiest way to get help. If you or someone in your group is hurt, calling for help avoids having to figure out an evacuation plan. If you are lost, rescuers can possibly determine your whereabouts by your description of the area.
It does not matter if it is 100 degrees Fahrenheit during the day. If you are stuck overnight in the wilderness or the weather suddenly changes, it is bound to get colder. Packing a jacket that keeps you warm and dry is essential to wilderness survival. Bring something that is made of a synthetic material rather than cotton. As Princeton University's Outdoor Action points out, cotton retains moisture rather than expels it and is difficult to dry. You can also use a jacket as a makeshift sling by putting the elbow of the injured arm in a sleeve, then tying the sleeves together.
A simple first-aid kit is also important for any wilderness outing, regardless of the length. Many outdoor retailers have first-aid kits small enough for a day hike. Some of the things to include in the kit are sterile gauze and bandages, ibuprofen or other painkillers, ointments and antibiotics, and medical tape. As a supplement to the kit, you might also bring SAM® splints, which mold well to broken limbs and are easily packable. You can also use a roll of duct tape to fashion splints out of materials found in the woods.
Matches and Lighter
Starting a fire is sometimes imperative to surviving the night. You can find kindling and logs to start a fire, but without the means to get a blaze going, you are in for a cold night. Bring both a lighter and matches. If one of those fails, you have a backup. Keep both of them dry.
A knife can cut strips of fabric to use as bandages, saw through twigs to make a fire, cut open packaging and, generally, make a bad situation easier. It is best to choose a Leatherman or Swiss Army Knife, which both offer a knife and other tools.
Food and Water
Bring more food and water than you think you need. Having extra on hand in case of an emergency can mean the difference between life and death, particularly in the case of water.
When darkness unexpectedly descends upon you, a headlamp is a wonderful thing to have. It provides light and keeps your hands free to perform tasks.