I use an army zippered up notpad thing. It has all the room I need for field notes. When I get back I enter them into a database program so I can search and do all that geek stuff.
I go thru fits and starts when it comes to note taking. The minimum I record is the zone range, what I am placing at what value and whether I think it needs N or N+or-. That and of course the holder number and side etc.