Everyone should be trained in First Aid. Backcountry first aid is a specific skill, since one cannot just stabilize the injury and wait for help. Help may be days in coming.
Professional first aid kits normally are cheaper than buying each item by itself.
Most injuries will be sprains, small cuts, blisters, heat exhaustion, hypothermia, blisters, hyponatremia, sunburn, and blisters.
Sprains are avoided by using good footwear and hiking sticks. Once a sprain occurs, usually wrapping it and using RICEI (rest, immobilize, cool, elevate, and ibuprofen) when not walking.
Small cuts are cleaned, debrided (all foreign objects flushed out) and allowed to dry, or protected if too large or if the limb must be used. Ointment can retard healing by keeping the wound moist. If ointment is applied, it should be placed around the cut, not inside.
Heat exhaustion occurs when people are dehydrated. Symptoms include nausea, headache, weakness, and sweating. People will be easily irritated and may lose motor control. Drink water, move into the shade, and moisten the clothing.
Hyponatremia occurs when people are over hydrated. Symptoms include nausea, headache, weakness and sweating. A lot like dehydration, except these people have been drinking massive amounts of water all day. Headaches are more likely with hyponatremia, and when it is extreme, projective vomiting as the body tries to get rid of the excess water. To treat, eat salty snacks and stop drinking water.
Hypothermia is a condition of lowered body heat. Usually it is damp and windy, but not necessarily really cold. Symptoms include shivering, chattering teeth, and loss of coordination. Remember: grumble, mumble, stumble, tumble. As the brain is affected, people get mean, then incoherent, then clumsy. If symptoms are mild, put on more clothing and get something to eat and drink. If symptoms are severe, the victim will have to be warmed with external sources (bottles of hot water). Under all conditions, get out of bad weather.
Blisters happen. To avoid them, wear boots that fit and good socks. Once an hour take the boots and socks off the allow the feet to dry out. At the first sign of discomfort, put tape on the rubbing spot. Once the blister has developed, either cover it with Second Skin or a blister blocking gel, or drain the blister and protect it with moleskin.