GitLab

• Block Entity Data <-- not really sure about this one... I THINK this is what you're using with the Spawner Item stuff, but this feature doesn't work in any version. Related to this bug report
• Blocks Attacks <-- Makes the item act like a shield, meaning it can block attacks when held.
• Bundle Contents <-- Defines the items and their data stored inside a bundle. Could be as simple as Item and Count. Great for custom reward bundles.
• Container <-- defines the items stored in a container item. Not sure how you'd implement within MM, but maybe similar to the Bundle Contents?
• Damage Resistant <-- allows items to be resistent to damage types tags, like #bypasses_armor or #is_fire for both as an item resistance and equipable damage resistances. Can be used to make items immune to lava, like netherite items.
• Glider <-- if present, this item allows players to glid as with elytra when equipped
• Instrument <-- specifies the instrument of a Goat Horn. Allows for custom sounds.
• Jukebox Playable <-- allows the item to be inserted into a jukebox and play the selected jukebox song ID.
• Lodestone Tracker <-- stores coordinate and world data for a compass to point towards.
• Max Stack Size <-- sets the maximum number of items that can fit in a stack. Between 1 and 99
• Note Block Sound <-- sets the sound event of the playerhead item when placed above a noteblock (like the ender dragon head, or piglin head)
• Repairable <-- allows the item to be repaired in an anvil using the specified ingredient

Personally, my list of priorities for these would be...

Glider, Max Stack Size, Damage Resistant, Repairable, Blocks Attacks, Instrument, Lodestone Tracker, Bundle Contents, Container, then the rest i guess lol.

Contik: Max Stack first, then glider and etc. Batarian: agreed^ Slipperysmurf: Stack Size, Glider, Blocks Attacks.