More specifically, can I bring a couple of boxes of Swiss chocolate with me? (going on Europe Contiki, will be departing London > AUS if that matters). If not, can I post it or something?

Should be fine. Just mark down that you have food on the form at the airport when you return to Oz.

Choclate is usually fine. Like Pervy said, just make sure that you declare it.

as long as the chocolate is in its orginal packaging its no problem at all,
i've done it a few times.

As long as the chocolate is packaged and the packaging hasn't been opened at all it isn't a problem. Just to let you know even if you post an item it still goes through customs and can be confiscated.