For a day out I'll use a small bag - a Wisport Sparrow 20 with a couple of side pouches does the trick.
In that I'll have a waterproof sheet to sit on (the local army surplus shop sold them as 'German Army waterproof sheets' - and great things they are too). I'll also have a small foam pad (cut from an old bed roll) for sitting on.
For cooking/brewing it will depend on a lot of things - where I'm going, what I'm doing, what mood I'm in. Either a meths stove or a gas burner, or maybe a collapsible fire box. Brewkit consists of a 1L nalgene bottle that sits inside a 750ml titanium mug. For food I'll either take a sandwich with me or, if it's a cold day and I fancy something hot, a pack of noodles or a frankfurter or something simple like that. Of course, you then need a pot or pan for cooking that in.
That will form the basis of what I take.
Then come the luxuries, which will depend on what I intend on doing that day.
A hammock is a good idea. It can be sat in or just to lay back and listen to the sounds of the countryside. Might take some whittling tools if that's what I intend on doing.
I'll also take a tarp/basha, but only if such weather is predicted or possible. Although in summer it's a good sunshade as well.
So, in looking at it, I'd say you've got everything covered for just a day out. It's too easy to over-pack and talk yourself into things 'just in case'.
Oh yeah, one thing you have missed out and no one's mentioned yet - a pair of binoculars and/or camera. Always have those with me because you never know what sights Mother Nature might offer you.