Artifact ring that provides a cocktail of basic resistances all at once (fire, cold, shock, poison, maybe sleep, maybe acid). This is interesting primarily because it is very useful early in the game and then becomes progressively less useful later on as the hero gets intrinsic resistances.

Could be named “The Ring of Everything Resistance” or “The Chromatic Ring”.

Puffer fish, a monster with a non-poisonous bite but a passive poison attack. Its corpse conveys poison resistance pretty reliably but is always poisonous to eat, even if it’s been tinned.

“The Amulet of Vitality”, an amulet of drain resistance that provides poison resistance and hungerless regeneration when worn and also increases your HP maximum by 20%.

Note: this could be implemented in a game that doesn’t have the amulet of drain resistance by instead making its base item the amulet versus poison and giving it drain resistance when worn.

New artifact The Scorpion Carapace, a suit of scale mail (made of chitin in any variant that has that material) that grants a 1d4 poison sting to the wearer’s attack chain and confers poison resistance when worn. Enchantable to +7 safely.

Artifact chaotic amulet Amulet of Splendor: provides every single amulet effect, as well as unchanging-ignoring controlled polyself when invoked. Wearing it conveys life saving (this WILL disintegrate the amulet if triggered), magical breathing, unchanging, poison resistance, ESP, reflection, strangulation (doesn’t kill you due to magical breathing but maybe it makes it so you can’t eat food or something while wearing it, or it autocurses), restful sleep, and gender change for as long as you wear the amulet. Base type is a cheap plastic imitation of the Amulet of Yendor.