A Atomic RPG System Disposable Item is an item that the character will consume, or otherwise use to achieve a temporary effect. These are often potions, herbs, or other things a character will actually ingest to gain some benefit. Disposable Items can also be things like a grenade which is meant to affect enemies. In either case these Disposable Items are used up and destroyed.
For more information see the official Atomic RPG System Page on Disposable Items.