Tie wire....Zip ties.  A million uses for zip ties.  Headlamp bulb.
Can of Fix a Flat...Spare ignition key hidden somewhere.  A lot of the
other stuff but not the CVs, the starter or the alternator...You can go
lots of miles with a non-charging alternator....I tested it....went about
475 miles using my two batteries only, once.  I now carry some brushes for
my alternator as spares.   Also, make sure your spare and jack are workable
and the wheel lugs can be removed... Rescue Tape, for sure...saved me too.
I also carry an old antifreeze jug full of water for if I spring a hose
leak and must re-fill....usually have some in the tank from the sink...but
not always, hence the reserve jug under the bench ..

  Don Hanson