Under the Wack A Tiki, there are tikis. Destroy them and you will get a sock.
Go to the Goo Lagoon pier (Mr. Krab's fair). Go to the area where the tower bungee jump is located. Next to the food and drinks stand is a trash bin. Jump onto it, then double jump onto the food stand. There should be a sock on top of it. This may require a few attempts.