The field books I use for work (at least the ones the office provides ...engineer here) are lttle white hardcover bound things that are really marketted for the surveyors trade. Fit well into a vest pocket on most of my wind jackets, or the front of my camera bag.
The really premium one I take out in potentially inclement weather is a plastic jacketted 6 ring binder that holds about 4x6 pages. The pages are made by J.H Darling , and are waterproof, and can be written on in the pouring rain with a soft pencil or waterproof pen, although the water drops from the rain cause some blurring of the waterproof ink until its carrier evaportes, so I prefer the pencil.
Look at a their web site called RiteintheRain.com.
I also use this paper in 8.5x11 size to photo copy sections of maps for when I am off on a hike backwoods taking photos. No reason that forms could not be photocopied onto this paper before putting it in the binder.