Basically if the car is in good mechanical shape, and within tune it is extremely rare to have the car die on you "in the middle of nowhere". Key is to keep up the periodic maintenance, and take care of minor things before they become MAJOR things.
For the engine to run, you need fuel, spark, and compression. Admitted all have to happen at the correct time, but for most road side repairs we will deal with the more common items.
WHAT TO DO when your Roadster will not restart:
To make sure the cap and rotor are OK, if the coil wire test passed, pull the wire off a spark plug, insert a paper clip into the spark plug boot, and repeat the test (plug).
IF OK, go to FUEL Test:
If no spark is present, then remove the distributor cap and check the the ignition points and wiring.
A simple "light bulb tester" can confirm there is power at the ignition coil, and that the points are functional.
Clip the light bulb tester across the ignition coils "+" and ground. With the ignition on, the bulb should light. (If not, the ignition switch, or wiring has a problem... you can "hot wire" the car by placing a jumper wire from the battery "+" terminal and "+" wire on the coil.
Now clip it across the "+ and "-" terminals: When the points close, the light should come on, when the point are opened the light goes off. [Check the points, make sure they open and close, and the wiring is connected.]
It that checks out, the coil is probably at fault. MOST electrical problems are just dirty & loose connections!
By holding the float housing upside down, and blowing through the fuel inlet, you can check the function of the flow being on or off by the position on the tab connecting to the needle & seat. Sometimes just blowing air through it will dislodge any particles. Check to see the float is actually floating in the remaining fuel (brass style floats) or the plastic style (later roadsters) are not saturated with fuel.
IF OK, remove a fuel line, and hold it into a can or plastic bottle. Have a helper crank the engine, you should see steady pulses of fuel come out. If not, check the fuel filter. If fuel is not getting to the filter, then it may be a bad pump, or a blockage (rust in the tank is most likely).
A bad pump may have some dirt lodged in the inlet or exit valves. (It is fairly rare to see a pump fail. When the diaphragm tears, they will leak fuel out the bottom vent hole... quite noticeable. Most "bad" pumps I've fixed by checking the inlet and exit valves for dirt.) Rust, or other junk, in the tank may be temporarily displaced by BLOWING back into the fuel line (remove the tank cap, and listen for the air coming back through the fuel tank). Usually this 'fix' is temporary, but may allow you to drive home before removing & cleaning out the fuel tank!
I recommend the utmost care when "blowing" into fuel lines. (not only can swallowing fuel make you quite sick, it could be deadly). Air hose is best, but when out "in the middle of no where" difficult to find!
Also It is always a good idea to have the battery securely mounted. On one event, one roadster had a loose car battery tip over and SMASH the distributor cap! Thankfully someone else had a spare cap to get the 1600 on its way again.
WATER in the FUEL: If the car seems to be sputtering when running at highway speeds, take a look at your fuel filter. If there is water in the filter, it will remain there... until you get up to higher engine speeds and some of it makes it down into the carbs. One reason it is always a good idea to either store the fuel tank completely full, or empty with the gas cap off to premote air circulation. [Thanks to Chris Coker for the tip]