There is a small group of items that will decay but can't be stored in a Preservation Box, or even be removed from your inventory to any other kind of container - the Abyssal gear pieces (Abyssal Bow, Maul, Helm, Mail, Leggings, Gloves, Boots) - that you can craft at a Circle of Power if you've learned sorcery during your journey. These Abyssal gear pieces can only be kept for longer if you equip them in your character and kill NPCs or players while having them equipped, so the decay timer will increase. If the timer of each Abyssal item goes down to zero, it will decay and disappear from your inventory, like any other perishable item you can actually place in a Preservation Box. The Abyssal gear pieces can also be lost upon death.