my mobile car/trackday/race toolkit is:
metric sockets
3 sizes of ratchets
metric allen keys (t-handle and socket-type)
metric wrenches
torque wrench
speed wrench
huge crescent wrench
assorted pliers/cutters
assorted MC hammers
assorted fluids (brake, oil, chain, cleaners, rtv, wd-40, simplegreen)
mity-vac, safety wire, zipties, ruler, metric tape measure, shop towels
gloves, rubber & mechanics
headlamp/flashlight
bike pump
and it all fits in 16"x8"x8" toolbox and one milk-crate, except the bike pump