Some kind of elementary repair kit is a good idea. At least a couple of safety pins (they were called "Wyoming buttons" when I was a kid), a needle big enough to thread dental floss through (also useful for removing slivers), a small amount of some kind of Tenacious Tape (duct tape doesn't work on silnylon, although I do take duct tape too).

I've used the safety pins to replace busted zippers and as clothespins. I've had to sew a busted strap occasionally. I'm always worried about sticking my trekking pole through the peak of my tent ever since, as phat knows, I actually did it once, while cleaning up a tent I was selling to him. I therefore take a sticky silnylon patch that came out of a McNett repair kit.