A while back I wrote about a somewhat more detailed version of the rules for foraging and hunting from the Expert Set. Forget all of that. This is better.
Foraging: When a party is travelling through an area that has a decent amount of plants growing in it that humanoids can eat, there is a 1 in 6 chance that the PCs can collect 1d6 rations of food per day by simply picking up what they spot growing next to the trail they are travelling on. If the party includes characters with special wilderness skills, they have a 2 in 6 chance to find things they can eat.
Hunting: When a party is staying at one campsite for a whole day, they can send out hunters or hunting parties to hunt for food. At the end of the day, each hunting party returns with 1d6 rations of food (1d8 if the party includes a character with special wilderness skills). While the hunters are out hunting, a wandering monsters check is made for each hunting party and for the camp.
Water: Unless otherwise specified by the GM, the party comes across sufficient sources of drinkable water each day they travel through the wilderness. No rations of water have to be consumed at the end of the day. (Assume all characters refilled the water rations they consumed during the day when they had opportunities.) Characters spending most of the day inside dungeons do not have access to sources of water unless the GM specifies otherwise, and must consome a ration of water at the end of the day.
Lack of Food: Characters who do not eat one ration of food in a day, suffer 1 hit point of damage and can not heal damage naturally without magic.
Lack of Water: Characters who do not have one ration of water in a day, suffer 1d4 hit point of damage and can not heal damage naturally without magic. After 3 days + 1 day per CON bonus, the character dies.
The idea here is that in an average wilderness environment, parties will not have much trouble keeping themselves fed by hunting, but replenishing their supply of rations will either take a considerable amount of time or require splitting the hunters up into several smaller groups. Both options mean an increased number of wandering monster encounters before the party makes it back to a town or their base. It’s a very simple mechanic but gives the players a lot of variables they have to pick, like the amount of food supplies they keep, how they pack them among their PCs, hirelings, and pack animals, at what point low supplies might be a reason to turn back, how to split the party, deciding which hirelings to send into the woods to uncertain fates or who to leave behind to guard the camp, and when it might be worth it to keep pushing ahead while starving instead of stopping to hunt. I see a huge potential for amazing unscripted adventures simply because a randomly encountered wyvern made off with the mule carrying half of the party’s food.
Extensive playtesting will be needed to dial in on the best die to roll for the amount of rations provided by hunting so that it severely inconveniences the party without getting it completely stuck and unable to continue towards their destination. But otherwise I’m really excited to give this a test run.