Here's what I started doing last year:
1) Using some online tool (I use Google Docs) I create a spreadsheet before every event. There I list all the work I have to do, as well as my final track setup. Using that I can look back and see what alignment and suspension setups I started with last year at the same track.
2) For the track, I made a double-sided note sheet. The front side has:
2.1) Track, Day, Session, Time, ambient temp, weather
2.2) checklist for getting on track (add fuel, torque wheels, charge camera batteries, etc)
2.3) Basic setup stuff (tire pressures, shock settings, spring rates on the car, etc)
2.4) Changes to be made from the last session (Went up 3 clicks of rebound, down 2 lbs of air on the right side, etc)
On the back side I have
3.2) Tire temps and pressures
3.1) Driving impressions (Loose off, pushy, I love it, whatever)
3.2) post-session weight
3.3) a section for all of the stuff from the first page, but I don't seem to fill that out often (camber, shock settings, whatever- they generally don't change during the session)
What I haven't done a good job with, is taking my track setup sheets and organizing them electronically. Basically I have to rifle through my notebook to see track notes from prior trips. I just organize the notebook by track.