Should I negotiate my severance? - any advice?

My manager said the package is final, but the letter gives me time to review. It has been weighing on me all week. 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.

Read the release carefully. Mine included things I did not expect, like a non-compete.