It's always changing and frequently not as well organised as it should be but at the moment:
MR2: Spare wheel, jack (but not the wheelbrace or jack handle

) OEM wheelnuts for spare.
Galant: Spare, factory toolkit, jump leads, tow rope.
Always used to carry a can of fuel in the MR2 as it was easy to stow in the front boot with the spare and other odds and ends. Can't really find anywhere to put similar stuff in the Mitsi as the boot is so cavernous that it'll just rattle around in there. Theres a bit of storage under the boot floor but it's not really deep enough.
Later this evening though I'll be stocked up with my full 'race kit' which will allow me to repair virtually anything I might need to do at the track.
EDIT - Thought I may as well include the 'comprehensive' list. (from memory so I might have missed something):
'Sprint box', containing:
Footpump, 3x hammers (big, little and a rubber mallet), 2x breaker bars (large and small), multimeter, copperslip, tie down straps, tie wraps (3 sizes), gaffer tape, Haynes manual, spare brake pads, Oil, Coolant, Brake/Clutch fluid.
Small toolbox containing:
Comprehensive socket set (standard and deep sockets, short and long wobble extensions and ratchets in 1/4", 3/8" and 1/2" plus adaptors from one size to another), wheel brace, Ratchet spanners (19mm, 17mm, 14mm, 13mm, 12mm, 10mm, 8mm), brake spanner (10mm and 11mm), Screwdrivers (Couple of Phillips, small flat one for prying, plus a huge selection of interchangeable bits with a handle), Mole grips (2 sizes), pliers, needle nose pliers and side cutters, tyre pressure gauge, 'magnet on a stick', numerous fuses and relays, jubilee clips, paint pens, head torch, electrical tape (black, red and yellow)
Trolley jack plus axle stands.
20l jerry can and spare set of wheels/tyres if required.