Informal:
* Not worth a dime: This means something is completely valueless.
* Cheap as dirt: This emphasizes how low the value is.
* Not worth the paper it's printed on: This is often used for documents or agreements that have no real meaning.
* A dime a dozen: This means something is common and therefore not valuable.
* Not worth spit: This is a very strong way to say something is worthless.
* A load of crap: This is a very informal and blunt way to say something is worthless.
More Formal:
* Of no consequence: This is a more neutral way to say something is unimportant.
* Without merit: This implies that something lacks value because it lacks quality or justification.
* Insignificant: This means something is too small or unimportant to consider.
* Futile: This implies that something is hopeless and will not achieve any result.
* Worthless: This is a direct and straightforward way to say something is without value.
The best phrase to use will depend on the context and the level of formality you need.