Top tools:
Breaker bar
Angle grinder
HSS drill bits
Rivnut gun
Spanners
Sockets
Jigsaw
Big vice
Wire stripper
Soldering iron
Step drill bit
MAPP gas tourch
Magnet on a wire - you will drop stuff in difficult places!
Break pipe flare
Break pipe bender
Hammer
I'll add more if I think of them.
Really nice to have stuff:
Compressor + air tools (got one of these after the car was done, wish I had gotten it earlier)
MIG welder
Lathe - made some custom bits for the interior on this
Hydraulic press (for bushes)
Engine hoist + stand
For E36 and later a laptop + carsoft for analysing error codes