A luck item is a general term for any item in NetHack that changes your Luck and/or Luck timeout, such as a luckstone. Some artifacts can "act as a luckstone" when carried, and function in the exact same way as one in addition to their other effects.
List of luck items
Since all luck items in vanilla NetHack outside of the luckstone are quest artifacts, the ability to obtain a luck item can render the guaranteed luckstone within Mines' End redundant. Some characters whose role this applies to may elect to postpone their trip to the Gnomish Mines in favor of Sokoban, for example, or else choose not to proceed beyond Minetown; other players may want a luckstone to tide them over until they obtain their quest artifact.
There is usually little tangible benefit to carrying multiple luck items in open inventory - spare luckstones can be kept within a container in the event your primary source of Luck is cursed. While an uncursed luckstone can suffice in most cases, blessing one allows bad luck to time out and provides a buffer against the curse items monster spell and other similar effects. Other luck items may be preferred in the main inventory over luckstones due to the benefits from their base items: all of them are intelligent quest artifacts that will resist the curse items spell 80% of the time, so blessing them is an unambiguous boon, and the quest artifact for your role will always be generated as blessed.
Some variants include other Luck-altering items that may function differently from a luckstone - see Category:Variant luck items for a list of these items.