Lots of good stuff in this thread. Depending upon the circumstances, I sometimes add:
- Chrono (likely uses the same tripod as Video Cam in earlier post - Lowe's has one for less than $30)
- Pull cart / garden wagon (depends upon if parking is close; also serves as a good umbrella stand or base for a work surface)
- Bungee cords (goes with cart)
- Cooler w/ ice
- Small pistol case/bag (if you are in a state that has cumbersome transportation requirements, and you don't want to drag a locked pelican case to the safe area)
- Box of nitrile gloves (in addition to wet-paint-steel-setting work gloves, above)
- Purell
- Chap stick
- Glock magazine baseplate removing tool (if applicable)
- Extra grip tape
- Q-tips (cleaning kit)
- 5-gal bucket for brass & shell sorting pans (works for a whole squad; too lazy for ziplock bags)
- Brass wand/roller/picker-upper-thingy
- USPSA rule book (particularly to resolve arguments at the bar after the match)
- Cold hard cash (sometimes due to the item above; also useful for food vendors and buying spare parts you didn't think you would need)