VFR I assume?
just a simple A5 plog is usually enough, so an A5 board should be fine. having the relevant airfield charts to hand is good, you can just buy a flight guide, i find AFE better than pooleys, and have the whole book ready perhaps with post its on relevant pages.
I have a speed=distance/time table with common groundspeeds and distances. Makes diversion planning easy, you could google it or knock one up on excel with relavant speeds for your aircraft. 80-140 should cover most SEP.
the good thing about an A5 board is you can strap it to your leg and it doesn't get in the way. A4 is much better for IFR as there's usually more to write down, and more approach plates and things to have to hand.
I put a strip of velcro on my board, and the opposite on my pens so they're always to hand when I need them.