Well, everyone's got their own foraging rules. Here are mine. Feel free to steal.
When doing research for these, most house rules seem to be aimed at gathering food to supplement rations.
In my game, rations are an important limiting factor on how far characters can travel from home. They can only be purchased in town. Later, the players will be able to upgrade the quality of their rations to travel further, through a Steading Improvement.
The purpose of foraging in my game is to gather rare herbs or fungi, primarily for crafting.
For context, travel in my system is across an open-world point crawl. Each week the party starts in the town (called Caelfall), and can travel a maximum of 12 hours a day in any direction. They then have to spend 12 hours not traveling before they can do so again. Of this 12 hours, only 8 of them have to be spent sleeping – the rest can be spent adventuring/exploring/dungeon crawling.
Characters can also force march for an additional 6 hours (50% of their base amount), but after doing so they have to rest for 24 hours before they can travel again.
Being encumbered or using magic items can increase or decrease a character's speed, and certain items might increase the base number of hours a character can travel per day before starting a forced march.
I have attached my Wilderness Travel rules in more detail in a pdf at the end of this post.
The regions in my world are: the Northern Farmsteads (levels 1-2), the Flats (levels 2-4), the Steplands (levels 3-6), the Foothills (levels 4/5+) and the Wode (levels 2-10).
Foraging
Sometimes a party will wish to forage for a crafting ingredient or hunt for herbs with special properties.
Travelling characters can make one foraging check a day. They choose one region they have spent at least six hours travelling through and make a Survival check (defaults to 3-in-6). On a success they roll on the region’s Herbs & Fungi table (listed below) to see what they find.
A character can also choose to forage near a location (that is not Caelfall) without moving. Each hour they spend foraging in this way counts as an hour spent travelling, but their location on the map does not change. Characters can forage for as many hours as they can travel (including forced marches). While foraging in this way the character makes one foraging check for every six hours they spent foraging. However, the character must also make one random encounter check for each six hours. Multiple characters foraging together do not have to make separate random encounter checks. For each successful foraging check made in this way the character can roll twice on the region’s Herbs & Fungi table and choose the result they prefer.
Regardless of the method, foraging is thirsty work and requires characters to consume an additional ration on any days they forage.
Design note: Foraging (and Crafting) is designed to be an optional system that sits alongside the main travel/dungeon-crawling loop. New players or players that prefer a simpler experience won't miss out by not engaging. If a group of players decide to forgo their normal weekly dungeon-crawl in order to find a specific crafting ingredient, I consider that a high enough cost to pay to be almost guaranteed finding their ingredient. Hence the foraging-in-place rules.
Herbs and Fungi
*: Taken from the game Dolmenwood (so not replicated here). If anyone is interested in my home version (with these included) feel free to DM me on discord.
M: Taken and modified from the game Dolmenwood.
Ash Berries: Found in the Flats, Steplands, Wode and Foothills. Small firm black-hued berries which taste harsh and bitter. Crush into a mushy paste, which can be dried to produce powder. The powder expands rapidly when disturbed, cloaking light sources and providing effective cover.
Bent leek*: Grows in the Northern Farmsteads. [Dolmenwood Player Guide]. 2 bunches can be consumed as a ration.
Blast Shrooms: Grow in the Wode and Mushroom Forest (underground). Explode if not handled delicately.
Bosun's Balm*: Grows in the Northern Farmsteads. [Dolmenwood Player Guide]. If eaten at breakfast: [Dolmenwood Player Guide]. The character's armour only occupies one slot for the rest of the day.
Braggart's Leaf: Grows in the Northern Farmsteads and Flats. A broad flat basil-like leaf, with large swollen cells filled with a strong-smelling oil. Causes a drunk-like effect in those that chew it; inspiring false courage and bravado. If chewed: Make saves against fear with advantage for 3d4 Turns.
Butter mandrake*: Found in the Steplands. [Dolmenwood Campaign Book]. 4 roots can be consumed as 1 ration.
Cotton Moss: Grows in the Flats, Steplands and Foothills. Dirty white moss clinging to the highlands, grows small beads which release a small burst of wind when popped. If eaten: Causes flatulence for 1d4 Turns.
Curnow's Sage: Grows in the Flats and Wode. A sage-like bush with silvery leaves. Brings clarity and relaxation. If chewed: Become aware if under the effects of an illusion or charm.
Elowen's Beads: Grows in the Flats, Steplands and Foothills. Small, rapid-growing succulent leafs with an intensely sweet taste. When ingested provide a small burst of energy and speed. Difficult to cultivate. If eaten: Increases speed for 1d4 Turns, +1 AC and +1 to attack rolls.
False Dandelions: Grows in the Northern Farmsteads, Flats and Wode. Small flower that appears as a golden dandelion, but when plucked wilts immediately – before it can be blown. If eaten: Causes an unearthly flush in the cheeks for 1d4 Turns.
Fenob*: Found in the Wode. [Dolmenwood Player Book].
Fire Peppers: Found in the Steplands and the Wode. Small shrub growing peppers which dry out easily, bursting into flame and crumbling to ash soon after. If eaten: Causes a dangerous rise in the body's temperature; requiring a Save versus Death or causing a fever: -1 AC, -1 to attacks and damage and disadvantage to all saves.
Gillywort*: Found in the Northern Farmsteads, Steplands and Foothills. [Dolmenwood Player Book].
Gingermellow: Found in the Northern Farmsteads, Flats, Steplands and Wode. A ginger-like root vegetable with smooth easily damaged skin. When ground and steeped in hot water seems to cure minor ailments. When steeped in hot water and consumed heals 1 HP.
Glowberries: Grow in the Northern Farmsteads, Flats, Wode and underground. Small berries similar to blueberries, which glow dimly at night. Easiest to find in darkness. Glow dimly, providing 5' illumination. If eaten: Causes the eyes to glow for 1d4 Turns.
Good Man's Snare: Found in the Flats, Steplands and Wode. An innocent seeming grey-hued mushroom with woody, pink-tinged stem. Releases a minty scent when broken. If eaten: Causes blind rage, inducing one to act rashly and without judgement.
Goodgilly*: Found in the Northern Farmsteads and Wode. [Dolmenwood Campaign Book]. 4 shrooms can be consumed as 1 ration.
Grue’s Ear*: Found in the Northern Farmsteads, Steplands and Foothills. [Dolmenwood Player Book].
Hag's Tears*: Found in the Wode and Foothills. [Dolmenwood Campaign Book].
Hell horns*: Fungi found in the Northern Farmsteads, Flats and Foothills. [Dolmenwood Campaign Book]. 1 shroom can be shared between 2 people as 1 ration.
Killer Bee Honey: Found in the Wode. Honey produced by giant killer bees. Gatherable by lighting a fire beneath the nest, pacifying the bees. If consumed: Heals 1d4 HP
Lankleaf root*: Grow in the Flats. [Dolmenwood Campaign Book]. 4 roots can be consumed as 1 ration.
Moon's Tears: Grow in the Flats, Steplands and Wode. Berries which grow on a rare shrub, radiating low temperatures which freeze dew upon their leaves. If eaten: Causes a dangerous drop in the body's temperature; requiring a Save versus Death or causing hypothermia: -1 AC, -1 to attacks and damage and disadvantage to all saves.
Moonhaw*: Grow in the Steplands and Foothills. [Dolmenwood Player Book].
Sallow Parsley*: Grows in the Northern Farmsteads. [Dolmenwood Player Book].
Satyr's Pipe Weed: Grows in the Wode and Flats. Broad green leeves with strange purple blemishes. Many properties; in particular capable of charming humans and luring them to sleep. If smoked: Sends the smoker and nearby inhalers to sleep within 1d2 Turns.
Shankroot*: Found in the Northern Farmsteads and Foothills. [Dolmenwood Player Book]. If cooked, 6 roots can be consumed as 1 ration.
Speckled Willow Bark: Found in the Flats and Wode. Small curling twirls of speckled bark. A folk charm to ward off fair folk. Dulls the tongue, reduces charisma, wards the brain. Distasteful to fairies. If soaked and chewed: Make saves against charm with advantage for 3d4 Turns.
Spirithame*: Grows in the Steplands and Foothills. [Dolmenwood Player Book].
Stonecap Shrooms: Found in the Flats and Steplands. Mottled grey–brown shroom caps which grow close to the ground, closely resembling pebbles. If eaten: Causes joints to become inflamed and painful for 1d4 hours, reducing speed by half and imposing disadvantage on all saves.
Wallow shoot*: Grows in the Steplands and Foothills. [Dolmenwood Campaign Book]. 10 leaves can be consumed as 1 ration.
WayfarrowM: Grow in the Foothills. [Dolmenwood Player Book]. If chewed: When the character engages in a forced march, they have a 3-in-6 chance of being fit for action the following day after only 6 hours of rest, instead of the usual 12.
Westernut*: Grow in the Northern Farmsteads, Steplands and Foothills. [Dolmenwood Campaign Book]. 6 handfuls can be consumed as 1 ration.
Whispering Weed: Grows in the Flats. Small tufts of grass-like leaves with stiff fines that brush against one another to cause a susurration. Causes humans to babble uncontrollably. If eaten: For 1 Turn forced to answer questions truthfully.
WolfsbaneM: Grow in the Northern Farmsteads, Wode, Steplands and Foothills. [Dolmenwood Player Book]. The sprigs only survive 1d2 weeks after harvest.