What you're used to, I think. When I was a young PPL student (in Boadicea's Air Force), I bought an American kneeboard, about A5 size, that I use for scribbling quick notes, QNH, etc on, and an A4 plogboard (not affixable).
That works well. I later bought a yoke clip to hold my IFR flight file (highly recommended) and stopwatch. With that, I find I have all I need to hand.
Charts I fold according to the Duncan McKillop method, and keep them loose.
I've seen folks with a board covered in bulldog clips, with everything apart from their lunch sandwich clipped to it. Didn't look right to me, but I suppose it's a case of what you're used to.