[sexobon]

Survival:

To help prioritize the necessities of life for any given situation, it's useful to remember that you can survive for about ...

1. ... 3 seconds without ammunition (in a combat situation).
2. ... 3 minutes without air (before losing useful consciousness).
3. ... 3 hours without shelter (in an extreme environment).
4. ... 3 days without water (before losing mobility).
5. ... 3 weeks without food (before wasting into incapacitation).

The Rule of Threes can help you determine what makes the weight cut when applied in order against your present or anticipated situation.