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

I was offered 4 weeks of severance after 4 years as a quality inspector, and I have a few days to sign. It includes health coverage for a couple of months. Did anyone negotiate and succeed?

Keep everything in writing and save the confirmation numbers. It saved me later.

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