In the original story, the idea of a lost city of gold, El Dorado, is central. It involves the journey of adventurers in search of this fabled place filled with riches. There are often elements of danger, like treacherous terrains and native tribes that may be hostile or helpful.
Some fanfictions may focus on the backstories of the characters in 'Road to El Dorado'. For instance, a story could be written about how Miguel and Tulio became such good friends in the first place. It could explore their early days, the events that led them to be the con - artists we see in the movie, and how those experiences shaped their journey to El Dorado.
A 'goodwill novel' is likely a piece of literature that focuses on themes related to good intentions and positive human relations. It could be a story where the main plot revolves around characters doing good deeds without expecting anything in return. Such novels often aim to inspire readers to be more kind and empathetic in their own lives. For instance, it may depict a character who volunteers in a community center and through their experiences, they change the lives of those around them for the better.
One idea could be a crossover with another adventure - themed movie like 'Indiana Jones'. The characters from 'The Road to El Dorado' could team up with Indiana Jones to find a new hidden treasure. Maybe they meet in a Central American jungle where they both are after different artifacts but end up realizing they need to work together.
Set a unique plot. Don't just rehash what happened in the movie. Maybe have them face a new villain in El Dorado who wants to take over the city in a different way. Or have them lose their way back home and have to find a new route, encountering new lands and cultures on the way.
In most cases, Goodwill doesn't typically take manga. They usually focus on clothing, household items, and electronics. But it's worth checking with your local branch to be sure.
Another good option might be Hercules. His superhuman strength could be useful in the dangerous situations that the characters from 'The Road to El Dorado' often find themselves in. And his more noble and heroic nature could either inspire or be challenged by the more roguish personalities of the El Dorado characters. They could work together to save a new world or find a new kind of magical treasure.
I'm not sure specifically what the 'goodwill watch story' is about as it could refer to many different things. It might be a story related to a watch and the concept of goodwill, perhaps about a watch that was given or sold with good intentions, or a story where a watch played a significant role in an act of goodwill.