All you need are the cylinders themselves and brake fluid. Strictly speaking you don't have to replace the shoes but if they're getting low-ish then you might as well do them at the same time. The rubber boot part of the cylinders is the bit it leaked from on mine, but when you get the unit it should be a pre-assembled thing so all you need to do is take the old one off via the two bolts it's held in with, then put the new one in and that should be it.
Replacing the cylinders is an easy task, but replacing the shoes I found was a bit of a pain but is worth doing yourself once. All the information you need to replace them can be found in the Haynes manual, and over in the UK it should be easy as to find.
---dens