my alternator shat on me whilst on the move - bad regulator - and it was night - time, I creeped the car home by removing the IP solenoid plunger with a spanner my mate bent with a torch and a vise - nutjob he was - but it took off the IP solenoid..
speaking of changing belts - I have had to change belts on a mates Golf with A/C on the side of the road - took about 45 minutes, good thing that we always keeped the engine sparkly clean..
tools were
combi spanners (10mm, 13mm, 17mm and 15mm)
allen socket - 8mm and 6mm
screwdriver = big ass one
both belts in
I have this plastic moulded briefcase of tools (german proxxon) that my mate gave me for a birthday - simple to stow not rattly and has everything you need in an emergency - combi spanners from 6mm to 19
sockets 8, 10, 12, 13,14, 15, 16, 17, 19, 21, 22 and 24
ratchet
wobbly
extensions
breaker tommy bar
pliers
wp pliers
hammer
wiring tester,
screwdrivers
allen keys 5,6,8 and 10mm
I sometimes keep it in the car along with a set of 500amp jumper cables I fabricated,
havent needed the tools much on the run but have helped other motorists many times..

parts i keep for car
1 40 amp bosch relay (too many relays in my car)
fuses
H/L bulb
drivebelts
little roll of this rubber that can patch rad hoses (works well for about 2 hours) I dont know that the hell it is (a crane mechanic gave it to me and its awesome)