If you could have one Nethack wish in real life, what would you wish for? This discussion has come up a couple of times - the most recent incarnation is here on Google Groups. The precise wording of the question was:
Lets imagine that you are outside and find a smooth stick. You, just playing around, pick it up and say "Zap!" Next thing you know, you have a handful of dust and there is a booming voice from the sky saying "You wrest one last charge from the worn out wand! The wand of wishing crumbles to dust! For what do you wish?"
In this discussion, I'm going to assume the following:
Thanks to Nikita Kazeev for several suggestions which didn't come up in the original Usenet discussion.
Items which in some way lengthen your (effective) lifespan are a very popular thing to wish for. The most obvious is an amulet of life saving (with the intent to wear it oneself all the time). We have to ask how well it works against death from old age, though. The best case would be that it makes you 18 again and hence effectively almost doubles your lifespan. However, in Nethack using up an AoLS only frees you from sickness if it would otherwise kill you next round, which suggests that if you have more than one life-threatening condition, only the one which actually killed you will be removed.
You might also want to give your AoLS to someone who needs it, or to sell it for a vast sum of money. The problem here is that it would be hard to convince anyone that it would work. Mark Grant suggests that the way around this is to "find some rich guy who's dying and tell him you'll save his life for a few million dollars payable upon survival". This strategy would also work for a wand of undead turning, with the added advantage that you could repeat the process until the wand ran out of charges.
It was suggested at a Nethack meet that there exist rich people who are gullible enough to buy an AoLS without any sort of proof that it works, but if you are skilled enough at conning people to pull this off, you could just as well sell them a cheap plastic imitation.
Another approach is to wish for some means of curing sickness, such as a blessed unicorn horn or holy water. These have the advantage that they can be used an unlimited number of times, unlike the AoLS which is strictly a one-use item. If all effects of old age fall under the heading of "sickness", then these items effectively grant eternal youth. Holy water has the further advantages that you can make infinite amounts of it and that you can trivially demonstrate its magical properties by dipping items in it and watching them glow blue. It has the disadvantage that if you're chaotic, drinking it will not cure your sickness, and will have a small chance of killing you. (Holy water does 2d6 HP of damage to chaotics, and a human tourist starts with 10 HP.) Since it's not clear whether in Nethack, "chaotic" means "evil" or "strong individualist who is somewhat distrustful of society", it may be safest to wish for a blessed unicorn horn if you suspect you are chaotic.
A blessed luckstone might save your life by protecting you from accidents, and would also be generally beneficial.
There are also items which do not directly extend your lifespan but allow you to do more in the same amount of time: speed boots and tins of orange dragon meat (for the sleep resistance). We can try to calculate which of the life-extending items provide you with the most extra free time.
The orange dragon meat provides you with 8 free hours every day to do whatever you want (that doesn't involve interacting with anyone else).
Speed boots make you 2/3 faster than normal. This could mean that they reduce your lifespan, making you "live fast, die young", but then nobody would consider them worth wishing for. So I'll assume that it means that you live 5 subjective hours for every 3 hours that pass in the outside world, you still need to spend 1/3 of your time asleep, and your objective lifespan is not reduced by this acceleration. (I'm also ignoring the problem of getting out of phase with the world if you are asleep for 8 subjective hours and awake for 16.) This means that you get 16*2/3 = 10 2/3 extra (subjective) hours awake every (objective) day.
If the amulet of life saving completely removes the effects of aging, making you 18 again, then it is better than orange dragon meat or speed boots, but if not, then it isn't very useful as a life-extending item. You might still want it as an insurance against accidental death or to sell, though.
Whatever you wish for, you can try to sell it. As mentioned above, you could get a lot of money for an amulet of life saving if you could convince the recipient that it worked. Wands would be easy to demonstrate, but they don't seem to have any advantage over guns and they have a limited number of charges.
You can simply wish for gold, which will gain you 5000 zorkmids. We can't know what the exchange rate for zorkmids is, but we can assume that they are pure gold and try to calculate their value that way. 5000 zorkmids weigh 50 "units", and since an apple weighs 2 units, a unit must be about 100 grams, and wishing for gold will give you 5 kilograms of it. The price of gold is approximately 360 US dollars per troy ounce (see http://www.kitco.com/charts/livegold.html), and a troy ounce is 31.10 grams, which means that wishing for gold gets you about $60000 worth of it.
You can also wish for gems e.g. "2 blessed diamonds". If we assume that a Nethack diamond weighs 100 grams, then this is likely to be the best way of getting money from your wish - 100g is almost as much as the world's largest cut diamond, the Cullinan I. Also, proving that your 100g diamond was real would be considerably easier than proving that your magic items really were magical.
Wish for gauntlets of power to have Strength 25 whenever you're wearing them, or two blessed potions of gain ability to give a smaller boost to all stats. Two blessed potions of gain level would provide a good HP boost, but unless your Constitution is very high potions of full healing would probably be better. A helm of brilliance, gauntlets of dexterity and a ring of adornment have also been mentioned, but unless you wish for them at +1, there is a risk that they will be +0 and therefore useless.
You could wish for a blessed figurine of your favourite monster, but there is a 10% chance that the resulting monster will be hostile, which for any reasonably "interesting" monster, would be fatal. One way to get around this is to wish for a blessed figurine of a kitten, and have some tripe on hand before activating it. Though Nethack's kittens are much stronger than real kittens, it would not be likely to kill you in the one round before you fed it, and perhaps it would grow up into a Nethack-style large cat.
Another possibility is a dragon egg, because dragons are invariably tame if they hatch while you are carrying the egg.
Some people seem to want a nymph or foocubus. You could also get multiple hostile nymphs by reverse-genociding them (this does not work for foocubi because they are not genocidable), but unless you want them constantly stealing from you, you had better be able to play the harp well enough to pacify them. Note that unless you have very high Intelligence and Charisma, sleeping with foocubi is potentially lethal.
Nikita Kazeev suggests that a church would be keen on an angel (preferably peaceful rather than tame, since in Nethack "tame" means "attacks everyone but its owner"). If we understood how a quantum mechanic renders the position and velocity of macroscopic objects uncertain, we could probably win a Nobel Prize in physics.