There's no point in doing anything but being polite and "professional"^1^ and doing so gives you the most leverage. If nothing else you can try to negotiate a higher severance. But it also potentially enables the best kind of "revenge".
Like the time I was laid off and instructed to revoke my and my team's access to systems. Yes sir... right away sir. Only the bean counters never verified that there was somebody left in the hand-off plan who could access everything.
Github admin? Not anymore. AWS root account? Who knows?
Honestly the fallout from that, including frantic begging emails for passwords about a month later, was far more entertaining than anything I could have said at the time. Best of all, the head bean counter got fired over it.
And because I was completely "professional" my boss there was super supportive and helped me get my next gig. Still checks in on me once in a while.
^1^ People often confuse playing the game to believing in it. Use it to your advantage.