For the so many times that I have experienced having car trouble, there are some parts that I really wish had then.  And, it was not only me, even relatives and friends were in trouble for almost the same parts while on the road.

The following parts are almost a must if not a must in every vehicle:

1. A good spare tire.  It means with a good tread, inflated to specification, correct size tire and rim.  I have seen many having the wrong spare tire and was just useless.  Even to a point that I had to lend my own spare tire.  Lucky for others who had low air or deflated spare tires, I had a portable air pump to lend or assist them with.
2. Fan Belts.  The important spare fan belt is the one that drives the water pump, alternator and power steering.  There was a time when I had to drive about 60 kilometers away from the city when my brother broke his main fan belt in the middle of the night.  Fan belt for air-conditioning is not that important unless you frequently drive through a desert.
3. Spark Plugs.  Fouled or faulty spark plugs consume more fuel and will tend to cause falter or fail.  When on the road, you will not have time to clean and re-gap them in case you get in trouble.  There are also times when a porcelain insulator inexplicably breaks.
4. High Tension Plug Cables.  If misfiring is not caused by spark plugs the next suspect will be the high tension cables.  Broken or cracked insulation causes trouble if not problems.  Current jumps from them before reaching the spark plugs especially when they are close to metal “ground” parts.
5. Headlight, Tail light and Signal or Turning light bulbs.  Sometimes head lights just burn out when you need those most.  Tail and Stop light bulbs are important to avoid being hit on the rear.  Well anyway, if you’re hit from the rear and tail lights are damaged, the offending driver will really have trouble proving your lights were defective.
6. Clutch cable.  Older cars will have a problem with this at one time or another.  Any part of the cable from the clutch pedal to the transmission could wear away and break without warning.
7. Fluids such as brake, oil, gasoline, transmission, steering and water are, for me, essential “spare parts” of a vehicle.  A car wouldn’t run, just simply conk dead or crash without them.  They are parts of the car and having a spare of them would be of great help. I once drove a car with a leaking hydraulic clutch for a co-medical representative for 250 kilometers aided by a liter of brake fluid.  Topping off the reservoir almost every 50 kilometers!
8. Radiator Hoses.  Upper and lower radiator hose as spares might be unlikely.  But when you get in trouble with one, it will only be then you would realize how much you need those spares.

An unbelievable “spare part” of the car is a spare driver.  This is important over long drives and time is of the essence.  I have seen several long haul trucks and passenger buses that have spare drivers.  If I am not mistaken, they have the spare or alternate drivers if a trip will be longer than 8 hours, non-stop or with only very brief stops.