Water (soundbite "H2O is betta") - In ideal conditions, like sitting on the couch with a comfortable 70 degrees programed into the A/C thermostat; an in shape person could last 4 to 6 days without water. Now add continuous running, extreme anxiety and stress, and depending on location, increasing heat or cold and that average drops significantly.So you need a supply of potable water.

According to the Mayo Foundation for Medical Education and Research "the average urine output for adults is about 1.5 liters (6.3 cups) a day. You lose close to an additional liter (about 4 cups) of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your total fluid intake, so if you consume 2 liters of water or other beverages a day (a little more than 8 cups) along with your normal diet, you will typically replace your lost fluids."

Keeping health, exercise (running screaming for your life), and your location we can say 3 liters of water a day will extend your life expectancy. Three liters of water weighs 6.6 pounds, which can get heavy trying to stay alive for weeks at a time. Camel baks are So you want to consider carrying water purification tablets.

A pressure cooker will boil water at 100 degrees Fahrenheit killing pathogens. "Boiling cannot remove chemicals having boiling points at or above 100 deg C (212F), nor heavy metal contamination, e.g., colloidal metal pollutants. Activated charcoal, however, can remove many pollutants, but can't remove pathogens. A combination of rolling boiling for one minute at standard atmospheric pressure (i.e., not in a pressure cooker) plus filtering with activated charcoal can neutralize most pathogens and pollutants."(Wikipedia) Check out http://en.wikipedia.org/wiki/Portable_water_purification for a good breakdown on all the nastys you can look forward too if you just lap up any water in front of you.