My advice would be to focus on the stuff that would really strand you,  
and also those things not readily available in the middle of "What's a  
Vanagon?" Country: fuel pump relay, fuel pump, ECU, hall sender or  
spare distributor, spare water pump belt, ignition switch (cheap).  
Those 2 relays in the box over the coil are pretty important, too.

Then there's the McGuyver-fix stuff like bailing wire, 16 guage  
insulated wire (like 30ft), various hose clamps, coolant and fuel  
hose, nuts, bolts, screws, duct tape, WD-40, and a good headlamp. a  
spare gallon of water of course. All depends on your level of  
McGuyver-ability, though.

And tools: sockets, 8,10,13,17mm wrenches, metric allens, vice grips,  
needle-nose, cheap multimeter,etc. Cell phone w/internet, for sure. I  
like to carry a soldering iron and solder - works off my 400W  
inverter.  Definitely the Bentley.

Stuff like cap, rotor, plugs, wires, fuel filter, thermostat, are  
unlikely to really strand you and are usually easily found - and you  
should replace all that stuff before leaving if it's suspect, anyhow.  
It's cheap.

Water pump - yeah, if you have the skills to replace it. I guess even  
if not, it would be nice to hand it to a mechanic, rather than waiting  
a few days for the shop to get one.

And as mentioned, whatever flavor of roadside assistance you can get  
is well worth it for peace of mind.

We're thinking about a trip down into Mexico, so this has been on my  
mind lately.

David