In my quest to get back to the basics of good old B/X (aka Moldvay/Cook) D&D, I've been perusing the Moldvay Basic set, and realized that there are a few things missing. These are not simply things that I would like to add for fun or realism or some other reason of arbitrary preference. These are things that it is strongly implied SHOULD be found somewhere in the official rules. Specifically, they are implied by a couple spells in the list of 1st level cleric spells.
Resist Cold: Without some basic rules for environmental hazards, this spell has only one use, which is to provide some rather trivial defense against cold-based attacks - and the only creature that uses such attacks in the Basic Set is the white dragon. The Expert Set adds the wall of ice magic-user spell and the frost salamander. Talk about your niche spells!
Yet there are all sorts of situations, both in the dungeon and later in the wilderness, in which characters might be exposed to the effects of extreme cold. If this spell didn't exist, it would be safe to say that the game designers were not concerned with any in-game effects of hypothermia, frostbite, and such. But it does exist, so what's supposed to happen to a character who goes climbing on a glacier in a toga and sandals, or who plunges into a cold underground pool to see what's at the bottom and then spends the next several hours wandering around the chilly cave in sopping wet clothes rather than stopping to light a fire and dry out? The rule book doesn't offer DMs even the faintest suggestion of what should happen. If the rules include no consequences for exposing a character to cold (other than the three aforementioned examples, which in most campaigns would be rare at best), then why would anyone choose to memorize that spell? I personally can't recall a single game, either as a DM or player, in which anyone did.
Purify Food and Water: If resist cold is an extremely limited niche spell in the rules as written, then this one is just out-and-out useless. So far as I can tell, there are no rules at all for the effects of thirst, starvation, or consuming contaminated food or water. Rations usually weren't a big issue in my campaigns, since few if any adventures ever went beyond a week of game time. Everybody just bought a week's worth of rations, and that was that. As far as I can recall, the only hint of a rule for food spoilage came in the Mentzer edition, with a note that standard rations spoil after one day in the dungeon. That's pretty much the extent of the thought given to rations by the authors and editors of classic D&D, but the mere presence of rations and the purify food and water spell in the rulebooks imply that there ought to be consequences for running out. What happens if you don't eat for a day, or three days, or a week? What happens if you give in to hunger and eat those moldy rations? The rules don't say.
Likewise, what happens if a character goes without water? Sure, in a lot of situations this could be hand-waved. Most temperate regions have rivers, streams, lakes, and ponds, and even dungeons have the subterranean equivalents, plus fountains and such, but what if the adventure takes place in a location that lacks these, or in which they're dangerous to drink? Since the rules were silent on the subject, it was easier just to assume that carrying a water skin meant you had enough water for the duration of the adventure, and never mind that a quart of water is a pretty meager amount even for a single day's adventuring. Lugging all that gear and treasure around a hazardous area, not to mention the occasional strenuous combat, is thirsty work, after all.
What should the rules have been? Since we're talking B/X, they should be fairly simple, without a lot of dice-rolling, if-then loops, repetitious checks to see if effects are avoided or reduced, and fiddling with half a dozen different stats in a quixotic attempt to model the effects with medical precision. As it happens, there's a pretty good model already in the rules which can be extrapolated for the effects of cold, hunger, and thirst. That model is the -1 penalty to all actions when characters fail to rest 1 turn in 6 during a dungeon crawl.
**Disclaimer: I'm a gamer, not a doctor! If some of these proposed rules clash blatantly with the facts of human physiology and medical science (at least more so than hit points fail to model wounds and fatigue), feel free to let me know and I'll consider revising them.**
Cold: Harm from cold depends on how severe the cold is, the character's clothing, and whether the character is wet or dry. Adventurers may generally be assumed to be adequately clothed for cool and even freezing temperatures. Bitter cold such as occurs in northern winters, high elevations, and ice
caves should require special gear such as heavy woolen cloaks or fur
parkas. Inadequate gear results in penalties which increase the longer a character is exposed. At such time as the accumulated penalties equal or exceed the character's Constitution score, the character dies.
Relatively mild cold weather, i.e. around freezing, results in a -1 penalty to all actions. As long as the character keeps moving, this does not increase. When resting or sleeping, the penalty increases by -1 per hour. A winter's night outdoors in nothing but one's underclothes could be lethal to the frail of health.
Extreme cold causes the -1 penalty per hour as described above when moving. At rest, this increases to -2 per hour. A night exposed on a glacier without heat or appropriate clothing will prove fatal to all but the hardiest of people.
Being soaked to the skin doubles the penalties.
Immersion in cold water can be deadly. According to wikipedia, water at 50 degrees F (10 degrees C) can cause death within an hour, and at freezing temperatures is often fatal in 15 minutes or less. For cold water substantially above freezing, penalties accrue at the rate of -1 per turn. In frigid water, the rate is -1 per minute. After leaving the water, the character may still suffer the effects of cold while soaked, as given above.
Optionally, for each 5 points in penalties, the character loses 1/4 of his or her maximum hit points. Bitter cold may cause permanent loss of digits or limbs to frostbite, at the DM's discretion. Hit points lost through exposure to cold can be regained in the usual manner, either through rest or magic.
Naturally, the resist cold spell renders its subject completely immune from all these effects. The spell should also immediately remove all accrued penalties; the penalty counter is "reset" and starts again from zero if the conditions of cold persist after the spell expires.
Warmth removes penalties at the rate of 4 points per hour.
Food and drink: For the sake of simplicity, a character must consume at least one day's
ration of food and one skin of water per day to avoid the effects of
starvation and thirst. There are two degrees of starvation/thirst: insufficient and deprived. For game purposes, insufficient is 1/2 of the usual daily requirement, and deprived is consuming a negligible amount. Each week of insufficient feeding results in a penalty of -1 to all actions, but after two weeks, the character's metabolism adapts to the short rations and the penalty does not increase further. Each week deprived of food inflicts a -2 penalty on
all actions, and there is no cap.
Each day of insufficient or no water inflicts penalties on the same scale, -1 or -2. In extreme heat, double the penalties.
penalties are cumulative, so a character who goes a week without food
and three days without water suffers a total penalty of -8. When the
total penalty equals or exceeds the character's Constitution score, the
character dies. Penalties are negated at the rate of 4 points per week of
proper feeding and 4 points per day of proper hydration. Increasing consumption from "deprived" to "insufficient" halts further accumulation of penalties, but does not decrease them.
In the case that a character is suffering from both insufficient food and water and exposure to cold, apply only the greater of the penalties, i.e. either the hunger/thirst penalty or the cold penalty but not both. In all likelihood a character will succumb to cold long before dying of starvation or thirst.
Impure food and water: No information is given in B/X as to the shelf-life of rations. The Mentzer edition rules state that standard rations spoil after one night in a dungeon, but are otherwise silent on the durability of either type of rations. I would revise that to say that standard rations remain viable for one week, half that in the dungeon, and iron rations are good for 12 weeks.
Here we must abandon the simple model of accumulating penalties. A debilitating illness of the digestive tract makes sense as a consequence for consuming spoiled or contaminated food and drink. This can range from the unpleasant but fleeting effects of upset stomach and bowels to really nasty stuff like cholera and dysentery. How sick a given spoiled consumable will make a character is left to the DM. As a guideline, mildly disgusting stuff like moldy bread or rotten fruit might, or mildly tainted water, causes gastric distress on a failed save vs. poison, resulting in a -1 penalty to hit and damage rolls for a day. Things that are notorious for causing food poisoning, like spoiled meat and eggs, might give a -2 penalty to all actions and halve movement rates for 1d6 days if the save is failed. Really nasty stuff, like water contaminated with sewage or a rotting corpse, has effects similar to the venom of a giant centipede, i.e. half normal movement rate and no other actions possible for 10 days. A new save is attempted at that time; if failed, the victim sickens and dies in another 1d10 days unless a cure disease spell or similar remedy is used.
If this is all too much for your game, simply declare that spoiled rations and foodstuffs are inedible and will not satisfy hunger, and anyone foolish enough to partake of severely foul food or water must save vs. poison or die in 1d6 days. Players will probably act as if this were the case anyway most of the time, so the above guidelines may be largely superfluous.
Poisoned food or drink, of course, inflicts the effects given for the poison, whether that be save-or-die or something else.
All of these effects are negated if the food or drink is purified prior to consumption.