These aren't really codes, but they are fun little secrets:

IN THE TOWN OF MELEE ISLAND

• Get the fortune teller to tell you your future.
• Talk to the pirate in the white shirt and ask him about Loom in the Scumm Bar.
• Talk to the dog in the Scumm Bar.
• Ask the Important Looking Pirates about what is in Grog.
• Play with the rat for a while near the Men of Low Moral Fiber.
• Walk into the alley when you hear someone calling from it.
• Try to steal from the store several times.
• Look at the sign near the clock and look at the clock 3 times.
• Walk through all the doors in the store.
• Let the rat out of the prison.
• Let yourself drown when you get thrown off of the dock (be sure to save first!)

OUTSIDE THE TOWN

• Look at the stump in the forest.
• Talk to Meathook before Elaine is kidnapped and ask him about his talking tattoo.
• Try to buy Stan's ships that you can't afford.

ON THE PIRATE SHIP

• Read the Captin's log about Toothrot.
• Threaten the crew and then try to tell them what you think "Keelhaul" means.

ON MONKEY ISLAND

• Walk to the far right of the heap o' rocks (this one is funny.)
• Sink your ship with the primative art.
• Tell the natives to look behind them for a three-headed monkey twice.
• Look at the skeletons on poles outside of the giant monkey head.
• Keep getting captured by the natives and getting traped in the hut. Keep looking at the door each time.

ON THE GOST PIRATE SHIP

• Board the ship before you use the eyeball necklace.