First aid (wilderness first aid in particular) can help a person survive and function with injuries that would otherwise kill or incapacitate him/her. Common and dangerous injuries include:
Lacerations, which may be infected
Bites from venomous animals, such as snakes
Sprains, particularly of the ankle
The survivor may need to apply the contents of a first aid kit or naturally-occurring medicinal plants, immobilize injured limbs, or even transport incapacitated comrades.