Food and Water
Most PCs need food and water to survive, and so when starting out on a journey, PCs typically need to stock up on provisions. Each day a character needs one ration of food and water. A ration of food can vary in price based on the quality of the food, but costs approximately 1-2sp per day. Water is often a free commodity.
As a general rule, it is reasonable for characters to carry enough food with them to last for a few weeks and enough water to last about one week without refilling, although more can be carried through the use of carts or pack animals. The Hunting and Survival skills may be used to gather food and water from the environment (DC based on the type of environment).
If a character is without food for too long, they begin starving. If too long without water, a character begins to dehydrate. Unless the environment is particularly harsh or the characters are running in a survival adventure, it is not usually necessary to track food and water consumption (it is just assumed that the PCs are able to stock up when necessary).
Starvation
Characters that have gone more than a week or so (GM's discretion) without food, risk starving and begin making hunger checks. At the end of a day without food, a character must succeed a Resilience check [DC 10], or gain 1 level of Hunger. The character must repeat this check every day until they are able to get sufficient food.
At the GM's discretion, if the character is exerting themselves (i.e. undergoing hard labor, forced march, etc), or if they have been starving for a particularly long time, a penalty (-5) may be applied to the Resilience Check. Additional, if a character is mostly immobile and calm during the day it gets a +2 bonus to the check.
Dehydration
Character that have gone one day without water (or similar fluids) risk dehydration and must begin making dehydration checks. At the end of a day without water, a character must succeed a Resilience check [DC 20], or gain 1 level of Dehydration. The character must repeat this check three times per day until they are able to get sufficient water (or similar fluid).
At the GM's discretion, if the characters are exerting themselves, are in a particularly harsh or dry environment (i.e. hot desert, etc), or if they have been without water for a particularly long time, a penalty (-5) may be applied to the Resilience Check. Conversely, if a character is in a comfortable and humid environment and remains mostly immobile and calm during the day it gets a +2 bonus to the check.