[pyroslev]

Aside from the obvious biggies and the robot with the bag n' tag form:

Enough tools and materials to rebuild the robot if it comes to it. If your team has built an exact practice robot, gut it to the frame and take all of the 'software'. If you don't use something, you can help another team out.

Batteries for everything times three.
Battery spill kit.
Battery Tester.
A small vacuum cleaner.
Everything that was in the KOP that you didn't use. (Useful to another team)

Anyone on the team who is taking their laptop should have the entire software of library on their laptop and the Driver Station Software just in case.

And if no one on the team has a WiFi hotspot or such service on their phone or tablet, PDANet installed so you can tether your computer just in case you need internet access. (A lot of venues disable WiFi and tethered internet connections lower interference risk.)