Severance offer, what should I ask for?

My manager said the package is final, but the letter gives me time to review. This is my first time dealing with any of this. I do not want to leave money on the table. Did anyone negotiate and succeed?

Read the release carefully. Mine included things I did not expect, like a non-compete.

I asked for two more weeks and a neutral reference. They agreed to the reference and added a week.