I keep all of the things Craig mentioned, plus about a foot long section of fuel line hose, small hose clamps for those and a couple of larger hose clamps, just because. Add to that a few spare marker/turn-signal/brake light bulbs.
One other items is a ziplock bag of a few various sized zip-ties. I've used them to tie something up out of the way like a wire that decided to drop down unexpectedly from under the dash, right in the path of my foot going to the brake pedal - yikes!
