When I were a lad it was a length of baler twine, a bit of wire, an old plug and a mole wrench.
In the Harley crowd it was a credit card and mobile phone.
Nowadays I carry a Swiss army multi tool, an adjustable spanner, wire, electrical tape, bulbs and a new plug.
What about you. Does your bike never go wrong or do you cart a spare magneto round with you?