The jet pack is a machine and one of the many inventions created by Sandy. It only appears in the episode "Spy Buddies."
It resembles a brown book bag with a little cone-shaped rocket on the bottom of it.
Role in episode
When SpongeBob and Patrick want to become spies, they receive many gadgets from Sandy. The jet pack is used by SpongeBob throughout the episode to consistently follow Plankton around with. It burns Plankton twice when SpongeBob gets too close to him.