Severance agreement arrived, need a second opinion

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. It includes health coverage for a couple of months. Did anyone negotiate and succeed?

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.

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