Disarming and hiding items - can I get them back?

[Legioned]

An enemy character handily disarms me of my lone weapon, then picks it up. The following turn he stows it in his backpack. What rules exist for me to recover this item? I am hesitant to use 3.5 rules or houserules, what exists in the current framework? All I am aware of is sunder.

[Pizza Lord]

Here's some advice to prevent the occurrence or to at least minimize the impact:

Weapon cords to not lose the item.
Locking gauntlets.

If he's placed your item in his backpack... I suggest punching him in the face until he either gives it back or falls unconscious.

Otherwise... use a cursed item that either keeps returning to your hand or one that considers him stealing it to make him its new owner. In which case... now it's his problem.

Almost forgot... Carry Another Weapon.

[Lost In Limbo]

Have your friends beat him up with their weapons.