Kelp Fries, sometimes known as Krusty Fries or Sea Fries, are a common side dish served at the Krusty Krab. They first appear in the episode "Greasy Buffoons."
The Kelp Fries look like normal fries. However, they somewhat resemble seaweed with the way they are shaped. They have had different appearances over the years. They are like French fries but in a Krusty Krab manner. Plus, they are likely made out of kelp or seaweed.
On some episodes, the quantity of Kelp Fries varies. An example of that is in the episode "Greasy Buffons" shown that the fries are 7 (or 8) in quantity while the episode "Kracked Krabs" has approximately 40+ fries on the platter. (However, these may just mean that the fries come in different sizes, the small box being a single serving while the large platter is made for a group serving.)
The boxes they are served in resemble those of McDonald's French fries since they are both red and contain the restaurant's logo in yellow letters on them.