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

I was offered 6 weeks of severance after 6 years as a customer-service rep, and I have a few days to sign. I do not usually post, so bear with me. I do not want to leave money on the table. What did you ask for?

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