Gummy is a giant ball of chewed gum that consists of a moldy slice of pizza, a pair of underwear, dirty socks, a used toothbrush, saliva, and other unsanitary items.
Role in series
"The Gift of Gum"
It is one of Patrick's greatest possessions. He gives it to SpongeBob on Best Friends Day. SpongeBob is disgusted by Gummy. Eight fish even resided in the gum, but SpongeBob eventually frees them.
SpongeBob hates Gummy so much that he tries to dispose of it in any way he could, which includes burying it and dumping it in a trash can. Later, SpongeBob, Sandy, and Squidward all are stuck in Gummy.
When SpongeBob gives it back to Patrick, he eats it, but then ends up burping Gummy out as a result of the hiccups he receives from consuming it. This leaves Bikini Bottom covered entirely in gum.
SpongeBob's Truth or Square
Gummy can be used to help SpongeBob get across in some levels.
There used to be a living pair of ripped underpants inside of Gummy that knew who Patrick was.
According to SpongeBob's Director's Commentary for the level "Hide And Sneak!," Patrick uses Gummy to store old socks, bits of food, kelp, and other things. When it reaches critical mass, it transforms into a "giant mass of putrescence."