There are not too many typical "spares" for autopilots. One could always carry an extra control head
and/or computer and/or linear drive
, etc - but you are basically carrying a whole extra AP by this time.
If your linear drive
is old, you may consider a set of brushes
for its motor
. The quadrant bolt listed in a previous post makes sense also. Maybe a rose joint for the end of the drive arm, since these sometimes seize.
If you would like a twofer, another compass
added into the system gives you backup for the chartplotter
Hopefully others with that system will chime in.