I know this is an old post but I'm sure people still see it.
Most GPSr do not update the direction unless you are moving. Sometimes when there is tree cover or bad signal, it is not always accurate. I think a good old magnetic compass is a good tool to have.
There have also been a couple times that I wished I had some TP. I won't go into those stories though. Baby wipes are actually great in case of "emergencies," or for just cleaning your hands, face, etc.
I also bring hand sanitizer and gloves for when I'm digging around in leaves, dirt, etc.
Some caches may require some wading or just have some really wet ground. It doesn't hurt to throw some rubber boots in the trunk.
This is my complete list that I have been working on.
1. GPS
2. Pen
3. GPS cables (For running GPS from cigarette lighter and for uploading points from GSAK)
4. Laptop with points loaded (I use my laptop loaded with GSAK for paperless caching.) OR
5. Papers with waypoint info
6. Compass
7. Flashlights
8. Batteries
9. Rubber boots
10. Gloves
11. Screwdriver or something long and metal (For poking and digging)
12. Tweezers
13. First Aid/Bandaids
14. Water
15. Camera
16. Baby wipes or TP
17. SWAG (For trading)
18. Plastic bags for CITO