Back in the early 1930's when mountain accidents were not that uncommon, The Mountaineers, a Seattle, WA based climbing club, studied the causes and what might have prevented or reduced the severity of accidents and increased the rate of survival.
They devised a list of ten items that should always be carried on outings. These items are directly related to increasing the likelihood of survival in case of accidents, etc. This list became known as the "Ten Essentials". The list has evolved over time from a list of individual items to a list of functional systems; the updated Ten Essential Systems list is included in Mountaineering: The Freedom of the Hills, 7th Edition.
In the links above, I give my rationale for choosing certain features of each item from the viewpoint of creating a practical kit, meaning one that is light enough to carry at all times, usable for a survival situation and reasonable in cost.
Jim Yuen, March 2002
revised Sept 2008