NetHack/Tactics with Items

Food
Eat these corpses:
 * wraith (level up)
 * giant (strength up)
 * mind flayer (intelligence up or gain the telepathy intrinsic)
 * floating eye (you get the telepathy intrinsic)
 * quantum mechanic (you get the speed intrinsic if you don't already have it, but lose it if you do)
 * blobs, jellies, fungi (F), gelatinous cubes and puddings (often hurts you a little, but a good way to gain intrinsics if you are observing vegan/vegetarian conduct. black puddings are not vegetarian. don't eat yellow fungi unless you can unhallucinate yourself.)
 * lizard (if needed; cures stoning, lowers stun + confusion to two rounds, will not rot)
 * unicorn (only eat unicorns that are not of your alignment, you can gain poison resistance, and help your alignment. these are also very good for sacrificing as well.)
 * dragon (gain intrinsics that that dragon has, so red dragons give fire resistance, black dragons give disintegration resistance, green dragons give poison resistance, etc)

Don't eat these corpses:
 * kobolds (sickens you, okay for any character who is poison resistant like orcs, barbarians)
 * bats and stalkers (stuns you for a while)
 * mimics (you can't move for a while)
 * cockatrice, chickatrice, Death, Famine, Pestilence (you die)
 * green slimes (slimes you)
 * your own race (cannibalism gives you the aggravate monster intrinsic unless you're a caveman or orc)
 * cats and dogs (gods don't like it, okay if you're a caveman or orc)
 * werecreatures (you become one, considered cannibalism for humans)
 * leprecauns, nymphs and tengus (you gain teleportitis, which unless you have teleport control, is very annoying because it makes you teleport to random places at random times)

As a general rule, if your pet will eat it, you can too. (Exceptions: pets will eat dogs and cats, and tripe rations aren't for human consumption)

Genocide
A blessed scroll of genocide removes all monsters with a particular letter. A uncursed scroll removes one single type of monster. A cursed scroll creates monsters of that type, which experienced players may find useful.

Genociding your own race is fatal

It's a good idea to genocide all kinds of liches (use a blessed scroll of genocide and take out "L"), because they are powerful spellcasters who can curse your items and summon hordes of nasty monsters.

Mind flayers and master mind flayers should also be genocided, because they eat your brain, causing you to forget what you've learned, and in extreme cases, to die from brainlessness. If your character is a dwarf, remember to use two uncursed scrolls rather than one blessed scroll!

If you have spare scrolls of genocide, consider getting rid of the following monsters:


 * Eels (can drown you, but can be avoided with careful play, an oilskin cloak, or an amulet of magical breathing)
 * Rust monsters and disenchanters (can damage your armour and weapons)
 * Olog-hai and other trolls (have the annoying habit of constantly rising from the dead, though a tinning kit or hungry pets can make short work of them as well.)

The Ascension Kit
"Ascension Kit" is a term experienced NetHack players use for the equipment they hope to have before entering Gehennom (Hell).

Ascension Kits provide extra speed (e.g. boots of speed or a spellbook of speed), magic resistance (e.g. a gray dragon scale mail, Magicbane or a quest artifact), reflection (e.g. a silver dragon scale mail, a polished silver shield or an amulet of reflection), boosted stats (e.g. Gauntlets of Power, Gauntlets of Dexterity, a Helm of Brilliance, any item of gain X), levitation (e.g. a ring or boots of levitation), something holding your stuff (a blessed bad of holding and an oilskin sack are nice), a pick axe for quickly traversing Gehennom's long, pointless mazes and ideally at least one amulet of life saving.