Which car?
Car1) A Turbo and a catalytic converter. A spare distributor and ECU.
Car2) An angle grinder, a chainsaw massacre mask, assorted papers from work, a spokey, some deoderant, a torch and assorted spare bulbs/wheel nut caps. And an OBDII code reader.
Car 2 often gets blankets, camping stoves and a few other things thrown in in winter in case I get stuck – that way I can true my wheels for days until found.