Brake Shoes / Pads
There are nowadays 2 main road brake pad sizes, generally referred to as "Shimano" and "Campag" fitting.
The other bit choice is between "normal" ie Alloy compatible brake pads and "carbon" ie for carbon rim use. The later are not made of carbon but usually some synthetic material which resists heat better as carbon rims do not conduct much heat away and hence braking temperatures are much higher than for alloy.
Finally there is the fixing method. Most quality road shoes are attached by an allen key. In Campag's case by a power-torque bolt which is better but a hassle if you haven't got the key.
Cantilever and V brakes tend to use studded shoes which are unthreaded.
As usual, ask if in doubt.