Over the past couple years I have started using my Scorecard Holder and Yardage Books when playing rounds. For courses I already know I don't use a yardage book and rely on my range finder and golf gps watch (Garmin S62). For course I am not familiar with I will purchase a yardage book (if available) in the pro shop and use my watch.
I also keep a couple note cards in the book which show my club yardages, wedge matrix for all my wedges (pocket, 1/2, 3/4 and full swings) and yardage calculations to account for wind & elevations.
I'm curious what other TT's members use to help them on the course or other notes they carry with them.