I can't believe I haven't answered this before...

I have a small notebook which I always bring with me in the field. It's 29 lines to each page, the size is about 3" x 8". There's plenty of space for notes about lens, exposure, contrast level etc. All my holders are numbered, so I'll jot down something like "4A-SY150/1/50:11-E4-17" which would mean "Holder 4 side A: Symmar 150mm at 1/50s, f:11, contrast range 4-17 on my Pentax Spotmeter". I would then know that this negative will require very careful development to keep the contrast under control.

The next step is to take all my holders into the darkroom and develop everything by inspection - but the inspection light is too dim to read my notes. I will also promptly forget which film came out of which holder, except the few that were in Linhof holders with numbering intact...