It somewhat depends on what you are trying to try out … if you want to know how an optimised system feels against a full Shimano set-up, then you need to use a full Campagnolo system including chain, chainrings, cables etc., set up by someone that is as familiar with Campagnolo as many mechanics are with Shimano.
If you just want to know how you get on with the different ergonomics of Campagnolo against Shimano, then there are corners that you can cut but in doing so you’ll be losing accuracy, predictability and smoothness of shift.
The absolute minimum you can *get away with* is probably rear gear, and shifters. The front shift won’t be very good but with careful set-up it will be workable, the rear shift (if you are running Shimano / SRAM 10s cassette at present) will be OK but possibly a bit rattly, probably worst through the middle of the cassette (where any derailleur system is at it’s most sensitive).
As you add in more dedicated Campagnolo parts, the shift overall will get better and more accurate. A full crank set (cranks, rings and BB so that you get correct chain line) chain and chain will make a big difference to the front shift. It needs to be set up correctly.
Campag cables assembled with metal ferrules and if you can avoid it, no in-line adjusters, make a big difference to consistency and accuracy of shift.
There are warranty considerations, too, depending on the extent to which they are important to you.
There considerations apply just the same whether you are looking at Campagnolo, SRAM or Shimano … systems are increasingly designed to work as just that.
HTH
Graeme
Velotech Cycling Ltd
Campagnolo Main UK SC