From the people who brought you the pet rock 2.0, comes something completely useless...yet necessary:

Only slightly more difficult to care for than the pet rock, your pet pocket cactus (under two inches tall!) is sealed tight inside its bottle, resting in magic blue gel which has all the nutrients the little dude needs to grow. Add a little sun and your cactus will thrive.

[$8-$10, ThinkGeek]

Related: Pet Rock 2.0