Old style Ronstan shackle key only, tied to the boat near the centreline. It can pretty much undo everything on the boat except beam bolts and we've never had a need for anything else. We've de-rigged once, pretty much completely, in the water with just the shackle key, after breaking a bow off.

Having said that, we never sail somewhere we can't rescue ourselves from, unless there are rescue boats around.

The local twelve foot skiff sailors carry a length of 6mm spectra onboard for emergencies.