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

My manager said the package is final, but the letter gives me time to review. 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.

Thanks for writing this out. I went through something close to it 9 months ago, and it got easier once I kept a simple log of every call and form.