It originated during the American Revolutionary War, referring to the Continental currency, which was the paper money issued by the Continental Congress. This currency quickly depreciated due to overprinting and lack of backing, becoming practically worthless.
Therefore, comparing something to a Continental dollar implied it was as worthless as the currency itself.
Here are some examples of how the phrase is used:
* "That old car is not worth a Continental. It's just a pile of rust."
* "His promises are not worth a Continental. He never keeps his word."
* "The movie was so bad, it wasn't even worth a Continental to watch."
The phrase is still used today, though it's not as common as it once was. It's usually used in a humorous or informal context.