The Dining Sock is an item that belongs to the Flying Dutchman. He uses the sock to eat with, and he cannot eat anything without it.
The Dining Sock is a regular blue-striped sock. It seems to be pretty durable since SpongeBob and the Flying Dutchman were pulling on it hardly. Though, The Dutchman tells SpongeBob to stop because he probably knew that too much pulling would "stretch out the elastic."
SpongeBob and Patrick steal the Dining Sock to prevent the Flying Dutchman from eating them. SpongeBob and the Dutchman fight over the sock until Patrick declares that they have reached an impasse. The Dutchman proceeds to give the two three wishes.