Severance offer, what should I ask for? - what worked for you?

I was offered 18 weeks of severance after 18 years as a web developer, and I have a few days to sign. I worked as a web developer before this. There is a non-disparagement clause. What did you ask for?

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