Having emptied and refilled the boot this weekend:
Air compressor (twin cylinder jobbie that was in the Defender because those tyres took a lot of air)
Tow bar
Shackles, tow rope, bungie cords, ratchet straps
Number plates
Jump leads
Rope (shakles usually too big to fit into small cars)
Small socket set
Dog bowl
Waterproof jacket
Shooting stick
Usually not left in there but usually in there: shotguns, rifle and machete along with ammo.

Really need to build a shelf unit so don't need to keep rearranging things when knackered, muddy dog goes in the back