Working as a messenger I have a few more tools in my bag than most, but they have all been usefull at some point.

Combo 15mm/ headset wrench(the headset part isnt a nessisary carry all the time tool, but its been nice to have a few times)
Small adjustable box
Patch kit(4 patches, tire boot, glue, sand paper, valve adaptor)
spare tube
Tire levers
hand pump(always works, unlike co2)
allen key set
spoke wrench
zip ties
tape