Should I negotiate my severance? (update)

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.

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

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.