Severance agreement arrived, need a second opinion - any advice?

My manager said the package is final, but the letter gives me time to review. Any experience at all would help. I do not want to leave money on the table. Did anyone negotiate and succeed?

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.

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