Who Finds a Friend Finds a Treasure (1981) on Netflix

Plot summary

A map showing where the Japanese army hid a war treasure at the close of World War II comes into the hands of Alan Lloyd, a gambler with debts he cannot pay who is already on the run from his shady employers. Gangsters want the map, so Alan hides aboard the boat of Charlie O'Brien, an actor hired to advertise a terrible tasting jam on a long promotional voyage. Alan adjusts the compass so Charlie has no idea where they are sailing. When Charlie finds him, the pair fight and tumble overboard, and they come ashore on a remote island they take for deserted, until they meet a group of natives.