Fiberfix spoke (or 2) instead of regular spokes so you can replace a broken drive-side spoke w/o removing the cassette. You can ride on the fiberfix long enough to get to a bike shop for a real repair. Make sure the multi-tool has a spoke wrench that fits your nipples.
Brake pads.
One brake cable.
A couple of zip-ties and a small roll of duct tape.
Forget the CO2 pump on a tour - you're going to need a pump good enough to top off your tires every couple of days anyway. Topeak Road Morph is great.