Grandma Worm's Gourmet Feed is one of many pet food items only seen in the episode "Gary's New Toy." It is a pet food for worms.
Grandma Worm's Gourmet Feed comes in large, dark yellow bags with the picture of an old elderly worm (that really does look like a grandmother) on it. The feed itself is yellow in color just like the color of the bag it comes in.
Role in episode
The Feed is first shown at the Pet Store when Patrick takes "free samples" from them. He punches a hole in the bag and starts to eat the feed. After SpongeBob and Gary leave, Patrick comes back and punches another hole in a different bag and eats from it again. The worm feed is not seen again after that.
This is the only pet food that Patrick actually steals (they were not free samples and he punches a hole in them and eats the food, it is both stealing and damaging of items).