Just got laid off, what should I do first? (update)

I lost my job as an accounts payable clerk and I am not sure what to do first. There are 4 people counting on me, so I am trying to be careful. I have a box of my things and a short letter about benefits.

Thanks for writing this out. I went through something close to it 11 months ago, and it settled down once I kept a simple log of every call and form.