It all depends how far your off the beaten track, if your near wife, transport, ect to get you home you don't need very much kit, but out on country lanes away from towns and no transport I carry all this, yes it seems a lot, but I have used all of these not only for me, but to get other cyclists home that carry nothing.

1 P*ncture repair kit
1 allan keys
1 set of tyre levers + 2 spare
3 inner tubes
Folding tyre
Tyre patches
1 small head torch in winter
marigold gloves
Small length of chain (3 inches)
1 small chain tool
Cassette tool and chain whip
Spare spokes
Kevlar spoke
hypercracker
Spare nuts, bolts, powerlinks
Wire cutters
Pliers
2 small screw drivers
Small sockets to fit screw driver handle
First aid kit with triangular bandage paracetamol, co-codamol, gaviscon tablets
Batteries for rear light and computer and bulbs
Small tyre pump (not mini)
1 Co2 pump
Zip ties
spare keys for house, bike locks
Phone
Pen and paper
10 sheets of kitchen roll
Very small bottle of hand cleaner
Insulation tape
£5 in small change
Small roll of gaffer tape
Brake and gear cables
Spare bite valve for camalbac
Small roll string
Spare gloves