Having been the one whose Mum died (10 years ago now) all you can do is be there. There really is nothing else you can do. Just give him a hug and be guided by him. Until you loose a parent you won't know how you or anyone will cope with it - my now DH cried long before I did.
As a PP said, keep the house running, I'd say get some snacky type food in, toast, cheese, cooked meats, crackers etc as food wasn't something I was overly interested in but I would eat toast.
I wouldn't buy flowers, people will buy you them - well intentioned because they don't know what else to do. I got that many I was sick of them, wanted to bin them, and rarely buy them now as I associate them with death and sickness (also got tonnes when I was very ill). I do still like sunflowers though.
Get onto the GP next week, they will give a sick note for bereavement so that work is covered. He may not want it, I've had colleagues come back in a day or two later, everyone is different. Many companies only give a couple of days, although my work were brilliant and I was told to take what I needed and not to bother, but I wanted them to have a plan too.
Remember you're grieving too, and be kind to yourself. It's ok to leave the hoovering and dusting etc for a bit, nothing will happen because you didn't run round with a Dyson.