Leathermans or multitool with pliers.
Set of metric combination spanners.
Spark plug socket with 3/8 extension and decent 3/8 ratchet (Facom ones have been pretty good to me).
Couple of 3/8 metric sockets to suit the common sizes (8mm, 10mm, 13mm, 17mm, 19mm, 17mm hex for gearbox plugs,I think?)...