Severance offer, what should I ask for? - 13 weeks in

My manager said the package is final, but the letter gives me time to review. I am in Cincinnati, in case local advice matters. I do not want to leave money on the table. Did anyone negotiate and succeed?

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

An hour with an employment lawyer cost me a small fee and made me feel much safer about signing.