Upon starting Hardcore Mode by finishing the quest "Stay a While And Listen…":
- All money and almost all items* aside from the Hearthstone will be completely erased from both the player's inventory and in the player's bank.
Edit: Apparently, this is mentioned in the yellow System text. Wow, do I feel like a dope.
- Worn armor and weapons with an Item Level higher than 5 or a level requirement to equip will be completely erased from both the player's inventory and in the player's bank.
- Any enchantments on any equipment** regardless of kind or source will be removed from equipment.
- The player's flight paths, professions, secondary skills, bank bag slots, and weapon skills will not be reset.
- Ammo bags and ammo*** will not be erased.
** Big thanks to the player who clarified this for me before I actually tested it! (You know who you are~)
*** Someone on Discord mentioned this but I don't know if that applies to all ammo bags and ammo.
I started an Alliance character and sent them a Battleworn Hammer, Brawler's Harness, Brawler's Pants, and Recruit's Boots (all Item Level 1). They also had a Small Silk Bag (IL 25). When I completed the Hardcore Mode initiation quest, all of my equipment stayed, but the Small Silk Pack and its contents (a Hearthstone) vanished without warning. This seems like something that players should be informed of beforehand.
I created a new character, then, and sent myself some Light Armor Kits to "enchant" my Squire's Pants and a purchased Tarnished Chain Vest. I was expecting the vest to vanish when I enabled Hardcore Mode, but to my surprise, it didn't. On this same character, I also purchased Mining, Skinning, First Aid, and Two-Handed Swords. None of these vanished.
On a different character I made purely I had gone to Ironforge and learned the "Two-Handed Maces" skill. I also collected the flight path while there. When I finished the Hardcore quest, I retained these things.
As for the flight path and bank bag slots, as well as items vanishing from the bank, I was informed by some people on the Discord server that this stuff happens. Or doesn't happen, in the case of flight paths and bank bag slots.