A snow globe is a gift sold by the Chumporium in the episode "New Leaf." It appears in other episodes as well.
There are two different types of snow globes seen in the episode, such as those that have a snowman inside and others that have a house inside.
Role in episode
Plankton sells a bunch of snow globes as part the grand opening of the Chumporium. SpongeBob even buys a snow globe for himself, but Mr. Krabs suspects that Plankton is using them somehow to steal the Krabby Patty secret formula by spying on them. Mr. Krabs then destroys most of the snow globes and Plankton kicks him out of his store.