Bundles never appear in a player's inventory, but are instead visibly held by both hands. This disables bonuses from weapons or off-hand items, and prevents the carrier from attacking. Non-attack skills can still be activated. Additionally, movement is usually slowed down while carrying a bundle, with the exception of ashes. Emotes are unaffected (though the bundle is usually visible while emoting).
While holding a bundle, a drop button appears on the interface, allowing the player to drop it. Equipping or switching a weapon or off-hand item will drop the bundle (including selecting the active weapon slot). Depending on what is being carried, the object may also drop if the holder is knocked down or dies.
Prior to the April 25th 2006 update, holding a bundle focused the aggro of computer controlled foes towards the carrier. Many groups exploited this aspect of the AI code by having the tank in their group hold the bundle and attract all the enemy fire while the less durable damage-dealers on the team such as elementalists could freely attack. The April 25th 2006 update removed this aggro-holding behavior.
For a list of bundles, see Category:Bundles.