Firstly let us Presume you are in a temperate climate. Extreme weather/climate conditions will be covered later.

Also that you are already on land, rather than in the air or on water.

Introduction

So when does a survival situation start, it can be general thought of as when your situation changes and disrupts you plans forcing you to spend longer in the open than you had original planned, probably overnight.

Triggers could be getting lost, yourself or a member of your party being injured, an expected change in the weather, vehical break down etc.

Seek Protection

Lighting a fire (TECHNIQUES) is a good moral booster it keeps you warm, dries kit and enables you to heat food and/or drink.

If you have any fatty food eat it before sleeping as your body will produce heat as a byproduct of the digestion process.

Administer First Aid