Everybody has their own method for handling foraging and hunting. I prefer to find the middleground between realism and simplicity. It's easy to confuse complexity for realism. Our living world is a highly complex fractal of perspectives, so the more intricate you make your gaming system the closer to realism you get, right?
This way of thinking makes two mistakes. First, it assumes realism is necessarily better. This is a flavor thing and I don't think I need to make comment on it. More importantly it argues from a mistaken position; that approximating reality requires many moving parts.
This is a bigger subject than I can fit in my brain currently. My own personal philosophy is that reality functions as a system of just-in-time rulings, much like a game of d&d. A wizard behind a curtain does it until you look, and then he quickly evaporates leaving only the panelboard for us to see. Rather than recreating the panelboard we only need to recreate the effect. If we have a reasonable facsimile that everyone at the table can agree is smooth, doesn't interrupt the flow of the game, and limits explanation and confusion, and reproduces the feeling and effect we want for this particular game, then we succeed. Let's move on.
What the Wilds are
The land outside human settlements is wild, untamed, and dangerous. It is inimical to intrusions from civilization and will resist in the most Yin way possible; be evading your assault. Chaos maps to the Yin principal; that which is dissolving, in shadow, inscrutable, evasive, destructive, consuming, passive. Law maps to the Yang principal - active, hierarchical, possessive, enforcing, knowable, penetrating, reductive. Yang reduces Yin to simple systems; it's what our science attempts to do by breaking the complexity of reality down into categories and then assuming those categories can be understood separately from each other. Yin is holistic; from the one comes the ten-thousand young, all interconnected by the source - it is unknowable. The land outside human settlements is, at its core, unknowable. The act of clearing a hex and setting up a stronghold is an act of 'taming' the Yin into Yang; it becomes map-able. But the Yin always tries to subvert your dominance in the form of monsters.
Finding Food
Nature is abundant and all giving, but it does not tolerate attempts to understand it. If you look for food you will find it, but there are risks.
Searching for Food
Takes a 4 hour watch or all day, depending on how you manage time. Everybody makes a Save. Those who fail find d4 rations worth of food, those who succeed find d6. Those who fumble incur a mishap; they accidentally ingest a poisonous plant, they're wounding while hunting, they get lost, gored by an elk, fall into a ravine, disturb a nest of hornets, etc. There's probably a d100 table writing itself right now. Those who get a critical success on a 20 find the maximum amount of food and can choose another teammate who is also rolling and increase their failure to a success.
Druids, Rangers, halflings, and frontiersman-types automatically find d4 food, d6 on a failure, and d6+6 on a success. They still suffer mishaps if they fumble because nobody is perfect.
Obviously, different locales will have different types of food and different difficulties in finding it. In a desert I would limit checks to only those who are familiar with the desert, as well as Druids and Rangers (not halflings). They can only ever find d4 rations.
While they're searching you should also roll an encounter for each group. Woe be to the ones who are attacked alone and lost. Hope you have a winding horn.
What Kind of Food is Found?
I would make d20 tables for every biome, if you care that much. If you're running a world that's vaguely European the list of familiar edible plants should be easy. There's about two dozen that are extremely common and easily identifiable. On high rolls I would say they caught rabbits, woodchucks, red deer, hedgehogs, raccoons, boar, or whatever else, as long as they're sufficiently equipped.
Working Together
Players that go into detail coming up with a good plan are more likely to succeed. If they spend time looking for tracks, finding deer trails, laying snares, or inquiring to locals about what plants are edible, I would more likely just give them the check rather than require a save. I might still check save to see if they fail utterly and get a mishap. The point is that if they're playing smart no check is needed, except to avert disaster.
But What about Starving?
The PCs are considered capable and competent. Any redneck with a gun can catch a deer. But if you over-hunt an area and abuse the Yin principle it fights back. Secretly roll some d6s. This is the maximum number of rations that can be extracted. If they push this boundary they get an automatic encounter as the Yin seeks to restore balance in Chaos. Druids will have a nightmare or omen foretelling the will of the Yin before it happens and will be aware through diegetic responses from the environment when the land is being abused. ("You look to the clouds, they look foreboding. You find a dead crow. The berries look like blood.")
