Severance offer, what should I ask for? - 23 weeks in

I was offered 16 weeks of severance after 16 years as a mechanic, and I have a few days to sign. It includes health coverage for a couple of months. Did anyone negotiate and succeed?

Thanks for writing this out. I went through something close to it 10 months ago, and it settled down once I kept a simple log of every call and form.