Personally
I always carry:
Breaker bar and 27mm socket & 19/17 mm for normal cars.
1 Litre 10/40 Engine Oil
PAS fluid
Brake/Clutch fluid
1 Litre Coolant
Various spanners 6mm+ an adjustable and some screw drivers, pliers and adjustable pliers.
5 ton tow rope + 2 x 3.25T rated shackles and a smaller D shackle for small towing eye's and an "ON TOW" sign.
Tyre pump
Tyre pressure gauge/tyre tread depth gauge (it was part of a set so it goes in the glove box!)
Cable Ties
Jubilee clips
6 x Bungee Ropes (for my roof bars)
Spare bulbs (for all light's)
Maglite Torch & spare batteries
Torch that runs off cig socket
Spare Fuses (all ampage's used in car)
2 x Blankets
1 Litre+ of fresh water
Dog Bowl's
Most importantly a pencil/paper and a mobile phone with enough talk time just in case ya get stuck.
For my family/dog's I alway's carry Wet Wipes (ya never know when they wanna crap), a few nappy's (for my toddlers in case it's a long journey) diluted juice and food.
If I plan a long journey then I add a fuel can & extra water, food & clothes and diff oil (leaky rear diff) & for when I ain't in the Disco or I can't bodge a repair to get home I've also got an RAC membership for my wife & I (for any vehicle
).