usually you get less than 5 minutes to gather your keys, coat and get the f-- off the property like a criminal when your let go. Plan ahead and just box your sh-- up now and take it home.
Don't sign the waiver, ask for a meeting with a upper HR manager and negotiate a better package something like your boss will be getting a few weeks later.
They probably could have kept you if they didn't blow all that money on stock repurchases...just saying.