I second the digital voice recorder. That's what I generally use when on "serious" projects with medium format. The Sony that I have is about the size of a candy bar and can record two hours of my silly blather. For me, this is way easier, a one-handed operation, than trying to scrawl stuff in a notebook while the wind flaps the pages around (not to mention more readily understood weeks later than my handwriting!)
The saved files can be downloaded as MP3s and stored "forever" on the computer, if desired. For the Bronica I record back number, film, lens used, meter used and date. I then note the subject, shutter speed and aperture, and any filter, plus any lens changes, and any unusual conditions for each frame as I go along. What I like about the recorder is I can also blather sudden thoughts -- 'note to self' -- that may or may not be directly related to the project. ("Should come back here and check out the old farm across the road some day.") I can record way too much info and edit later.
At home I transcribe the basic info into an Excel page for each roll. Some of the non-related stuff may go to a "to do" list or future photo project/destination list. Eventually the developer, time and temperature (and agitation), and maybe a one sentence assessment of the results, wind up on the page for a given roll.
If I'm just taking a few snaps on a hike with one of my folders, I may not bother with all those details. I still create a page for each roll detailing the subject matter.