There is not much to know about item entities as they are very straight forward. I’ll add any information people bring up and not go one by one through every single ent. Item ents make a good stand_in for other custom models you may wish to spawn. You can do this by overriding the model with a model keypair with the full path to the custom model.

Entity Description
item_bandolier Increases ammo capacity for weapons
item_breather Provides oxygen underwater
item_enviro Provides protection from harmful fluids
item_invulnerability Temporary invulnerability
item_pack Adds a large amount of ammo and increases carrying capacity
item_power_screen Adds 200 armor against energy weapons
item_power_shield Adds armor against energy weapons, drains cells
item_silencer Silences the sound of weapons

You may see this item in some jumpmod maps as a marker to show the way. This typically pops up in maze style maps, and some maps that are ported from other games/mods.

This is a special use item for jumpmod as quad damage also needs to be toggled with a mset. This can be done by the mapper by putting a mset keypair in their worldspawn ent along with quad_damage # (1-6) depending on how much you want damage to be multipled. You will also likely want to add rocket 1 to enable rockets or weapons 1 for other weapons.