Custom Items:

Repair Gems: Used to repair tools/weapons/armor. Right click the gem, and then right click the gear.
Charming Chisel: Adds a charm socket to any item, allowing the ability to add a charm to it.
Charm Extractor: Removes a charm from a socket (Has a chance to fail)
Silky Thread: Can be used to repair an Elytra (Has a chance to fail).
Crystal: Used to purchase items from the crystal merchant at spawn.
Fatal Bookmark: Separates a book with multiple vanilla enchants into several books.
Fragment: Can be used to craft relics and other custom items.
Relic: Gives a high level item/weapon/tool when opened.
Light Dust: Gives you Haste. Can be crafted using 8 Soul Gems and 1 Repair Gem.
Book of Tomes: Gives a random level enhancement scroll.
Timetraveller's Wristwatch: Takes you to the End (One time use).
Dimensional Compass: Takes you to the Nether (One time use).
Socket Chisel: Adds a socket to an item. Sockets are needed for enhancement scrolls.
Essence: 8 of the same essence create a tiered shady bottle.
Iron Giant's Heart: Has a chance to add a heart of life to an item. Has a chance of failing.
Dungeons Coins: Monsters on the Dungeons server have a chance to drop these coins. Use these coins at the Dungeon Trader at /spawn or /dungeons. You can combine 8 coins of one tier to get to the next.
Abyssal Steel: Has a chance to add AutoRepair to an item. Has a chance to fail or break the item.
Soul Gem: Used in Custom Crafting recipes
Grappling Hook: Right click to launch yourself in that direction once attached.
Clay Head: Right click to create a copy of your skin's head.
Arcane Scrubber: Used to remove useless enchantments from an item.
Infernal Scrubber: Removes useless enchants and turns them into a book for you.
Slime Bone: Tells you if you are in a chunk capable of slime spawns.
Mirror of Insanity: Has a chance to duplicate an item, downgrade it, or destroy it.