The basic necessities needed for treatment of minor discomforts to potentially life threating injuries can be neatly tucked away in a first-aid kit and should always be taken on any type of outing.  Below is a list that covers most bases for first-aid, but by no means covers everything.  Personal medical conditions, duration of outing, and size of group should be factors to determine what needs to be added to the list.

For backcountry treks these items need to be in a waterproof container and organized for quick findings and should include some survival items such as a signal mirror and whistle.  Also include your personal information in case you are found unconscious, incoherent, or deceased.