The Ten Essentials is a list of items recommended to have on your person when going outdoors. It was developed by the Mountaineers, a mountain hiking/climbing group based in Seattle, WA. Historically, the original Ten Essentials were:
A close observer will notice that the Ten Essentials provides a response to the Rule of Threes, in that it provides the basic tools to prevent overexposure, dehydration, starvation, injury, or even getting lost in the first place.
The Ten Essentials is a good starting place when deciding on equipment that you want to pack for an outdoor excursion. In fact, different groups such as the Boy Scouts have borrowed from and/or adapted the Ten Essentials to fit the circumstances that they are likely to encounter.