I always have in my backpack:
Destroy Field Rune
Destroys fire, poison and energy fields, from any distance as long there's nothing blocking the path. This rune is useful to escape from PK traps in PvP worlds and can be used to loot monsters that may be under the fields layed by other monsters. Also needed in a couple of quests.
Destroys movable objects. It can help you save you from a PK trap. You need to stand next to the item(s) you want to disintegrate. It will disintegrate up to 500 movable items (it will not disintegrate any dead human body, but it will disintegrate monster bodies). It does not count as an aggressive action, and therefore works in Protection Zones and does not prevent the player from entering them.
Amulet of Loss
If you die in PVP with the Twist of Fate blessing and wearing an Amulet of Loss, you will only lose Twist of Fate.
It is necessary to have it in backpack on pvp worlds.
The Energy Ring provides a Magic Shield for 10 minutes.
Stone Skin Amulet
Reduces physical and death damage by exactly 80% rounded up to the nearest whole number.
The Holy Tible
It allow to enter in The Pits of Inferno Quest.
Complete Opticording Sphere
It helps me to open portal in Opticording Sphere Quest
Scale of Corruption
Allows you to use the Teleport in the room under NPC Zlak (place it in the empty coal basin before entering the Teleport), which takes you to NPC Zizzle deep under Razzachai.
Scarab coins are decorative and also used for "sacrifices" (to activate warps) in the several Ankrahmun Tombs.
Can be used to pass the energy wall or fire wall in the Magician's Quarter Residential Area to access the Warlock and Infernalist spawns. It can also be used to enter the blue flame and access the Demons spawn under the Magician Quarter's Restricted Area.
Flask of Rust Remover
Can be used to remove the rust from Rusty Armors, Rusty Helmets, Rusty Legs, and Rusty Shields.
Needed to use the Gnomish Crystal Teleport System
Item obtained in the Heart of Destruction Quest. When used, it tells you where a vortex is currently active.
Golden Prison Key
Allows access to Prince Drazzak's
Bronze Prison Key
Allows access to Zavarash's chamber for 1 person. Use it on in the Roshamuul Prison when standing on the respective platform to be taken to him.
Silver Prison Key
Allows access to Terofar's chamber. Use it on in the Roshamuul Prison when standing on the respective platform to be taken to him.
All Knowing Sausages
When used a message will appear saying where is the portal for The Great Schnitzel.
Allow access to boss room in Forgotten Knowledge Quest.
Teleports you to the Adventurer's Guild if used in a temple.
Squeezing Gear Of Girlpower
Can be used as Rope, Shovel, Pick, Machete, Scythe and Sickle, but not as a melee weapon to destroy objects.
Blessed Wooden Stake
Can be used on slain Vampires in order to get Vampire Dust and on dead Demons to get Demon Dust.
An Obsidian Knife is used to get different types of leather from the dead bodies of certain creatures, such as Minotaurs, Dragons, Dragon Lords, Lizards, Bonebeasts, Behemoths and some bosses.
This item allow me to cut flowers in Issavi.
Blueberry Cupcake and Blessed Steak
It will refill your mana completely. It saved my life few times.
Wooden Key (Key:3940)
Used to enter/exit the Fibula Dungeon.
Silver Key (Key:0909)
The doors it opens give access to the external area of the Bastion and hence the boat that works as a shortcut between the Falcon Bastion and the underground area.
Copper Key (Key:3012)
Used for locking and unlocking the main doors to Hellgate.