This is always a hard one to answer. Mainly because it should be common sense to an extent.
However, im in no rush so I'll proceed.
I carry:
Spade, ground anchor, hi lift jack and bottle jack, multitude of strops, couple of nylon twist ropes for road towing, bridle ropes, shackles and snatch block, comprehensive tool kit, various spares Inc wheel bearings and seals, swivel ball plus bearings and seal, pot of grease, 2ltr gear oil, sachet of swivel ball grease, cable ties, rags, gloves (heavy duty and disposable), hand lamp and spot lamp, overalls and waterproofs, fire extinguishers, wd40, spray grease, waterproofing agent, wiring equipment and spares winch cutoff switch, bow saw, air compressor, hand winch (vehicle fitted with winch on front also), warm clothes, first aid kit, ratchet straps (handy for securing bodywork or loads etc), 10ltr water and cooking equipment etc when greenlaning, 240volt inverter, chest waders, various bungee cords and small straps etc, spare spark plug and distributor cap, handheld cb radio (vehicle fitted with cb also)
That's probably it I think.
You could say that you are never that far away from help in the uk, but in my view it's good to carry equipment.
You will very quickly learn what you should carry or need to carry after you have had some problems and learnt the hard way!
Cheers