Shenanigans of Luffy and Usopp PT 1 (?)

Usopp is left alone with his idiot captian, Monkey D. Luffy to keep watch of their ship, the Going Merry while the rest of the crew is out on errands. Oh no! The ship is too silent for comfort, causing Usopp to worry. What strange shenanigans has Luffy gotten himself into?