Gaffer's tape is another handy item in the bag. I've also started carrying a bunch of little spring clamps. Both are useful for things like attaching filters to lenses with no useful or odd-sized filter threads or holding a card to shade the lens or positioning a reflector for a still life setup and other things.
Addressing Ari's question--I've used the tools I carry for field repairs or when I'm traveling. Some have been as simple as tightening screws on a wooden camera or lensboard, and some tools are necessary for things like changing or adjusting quick release plates or on my Gowland PocketView for loosening stuck knobs or resetting knobs. I've removed and cleaned a groundglass occasionally.
On my Technika, the plastic guide plates for the Graflok slides are prone to fatigue, and if they crack, you can't use them to attach a rollfilm back or Grafmatic, and they can interfere even with ordinary filmholders used under the groundglass. A couple of times while traveling, I had to remove the cracked plates, put them together like a puzzle using tape to hold the pieces together while the epoxy cured. These repairs required a screwdriver, knife, and a tweezers. Eventually I had them replaced when I sent the camera for a CLA and I also got a couple of spares for field repairs.
I've also bought tools occasionally on the road as needed, and they've usually stayed in the bag.
and is left over from my geology studies some years ago.
