Here is a list which you can modify depending upon the reliability of the particular components of your own engine, and depending upon how remotely you wish to travel. For example, some yachtsman in remote cruising in remote areas with poor communication facilities and absence of workshops facilities might choose to carry a spare starter motor, spare alternator, etc ...
The engine manufacturers are usually willing to suggest a spares list for your own engine - which will benefit from their knowledge of those components most likely to require attention.
It may be a good idea to dry fit major components top make sure they are the correct parts for your engine.
Note: Cold Start not recommended for spares - usually contains ether which can damage the engine.