#adjust is the extended command to change the letter that represents an item in your inventory.
Consolidating Inventory Edit
A key function of the adjust command that is not immediately obvious is to force NetHack to consolidate identical stackable items into a single stack in the inventory. For example, if you are dipping potions with the intent of making holy water, you may start with ten different potions, each in its own inventory slot. Dipping them one at a time until they are fully diluted will leave you with ten separate potions of water, each occupying its own slot in your inventory. This is not a huge problem if you are using a water prayer at an altar, but is no good at all if you want to dip the diluted potions into a single potion of holy water that you already have. The answer is to #adjust one of the potions into its own inventory slot (b to b or whatever), which will cause Nethack to merge the other nine potions into a single stack. The advantage to using #adjust over dropping the items and picking them back up again, is that it will not use any turns to manipulate your inventory in this way.
A large part of surviving Nethack is forming good habits. One good habit is to be consistent with the inventory slots you select. When you have a replacement for your current weapon, for example, #adjust your new primary weapon to the slot that your old weapon occupied. An extension of this habit is to store inventory items in the same slot across many games. Which inventory slot is best for which item is a debated matter.
Preserving Starting Inventory SlotsEdit
When you start a new game, certain items tend to already be in certain slots. This is especially true if you play a small number of roles, or if you frequently play the very early game. Keeping those items in those slots saves you the time you would spend #adjusting all of your inventory items in the early game.
a - Primary Weapon - Your primary weapon always starts out being a. When you get a better primary weapon, adjust it to being "a" so you know it is now your primary one.
b - Secondary Weapon - Similar to using "a" as your primary weapon, most adventurers who start with a secondary weapon will have it labeled b.
Rapid Command EntryEdit
Another approach is to adjust key items to the inventory letter corresponding to the related NetHack command. For example, a Valkyrie carrying Mjollnir might put that weapon in the t slot, so throwing it is done by pressing t twice. The same would hold true for moving arrows to f. A player trying to wrest the last charge from a wand might adjust it to z to speed up the process.
Frequently-used items can be put on lower-case letters typed with strong fingers. The bag of holding, stethoscope, oil lamp, pick-axe, unicorn horn, magic whistle/leash, skeleton key, blindfold, tinning kit, athame, and ring of regeneration probably belong in this category.
Avoiding Inadvertent Command EntryEdit
In direct oppositions to the desire to rapidly enter commands stands the fear of accidentally executing commands. (this does not apply to those using the number pad)
Directional keys are pressed extremely often, and often after the (a)pply command has been activated. Examples of how this can be harmul:
- j - Crystal ball - 'asj' can transform (a)pply the (s)tethoscope south can easily become 'aj' (a)pply (j) the crystal ball.
- h - Pick Axe - 'ahk' becoming 'ahhk' transforms 'dig north; to 'dig west'
- y - avoid items whose use is so dangerous that the developers protected its command with a 'yes' prompt. This is also a directional key. Don't keep food in y - you might be standing over a cockatrice corpse.
- z - (z)ap your wand of create monster?
- a - (a)pply your crystal ball? Hope you were in a safe spot.
Mitigating Wand of cancellation damagesEdit
Placing a wand of cancellation inside of a bag of holding can be an extremely frustrating experience. Players who choose to carry these wands often keep their most valuable items outside of their bag of holding to prevent losing them accidentally. This preventive step is negated if the valuable item is placed in the bag in the same turn as the wand, assuming the valuable item has a lower inventory slot than the wand. Thus:
Z - An extremely valuable inventory item, like your wand of wishing 
Y - Another extremely valuable inventory item.
a - An expendable inventory item.
b - the wand of cancelation or the (b)ag of holding
c - the bag of holding or the wand of (c)ancelation
Visual Mnemonic DevicesEdit
Nethack often uses ascii characters which resemble the thing they represent. It is only natural that players would do the same. Similarly, you can use the same characters which Nethack uses.
Y - Stethoscope - "Y" looks like the item in question.
First letter Mnemonic DevicesEdit
Finding good Visual Mnemonic Devices for inventory items gets hard very quickly, so some resort to
p - Pick axe or other digging tool
- ↑ Debates rage whether you should carry your wand of wishing in the open at all. Wands of lightning, trapped chests, electric eels and energy vortices can destroy it, and nymphs can steal it, but in a bag of holding it is at risk if the bag gets cursed or exploded.