Severance offer, what should I ask for? (update)

My manager said the package is final, but the letter gives me time to review. There is a non-disparagement clause.

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

Thanks for writing this out. I went through something close to it 13 months ago, and it got easier once I kept a simple log of every call and form.