Cross country skiing involves a fair degree of exertion, more than down-hill, and 'body self-heating' will occur. In warm weather excess clothing should be removed (eg. into a back-pack, or left in the car) - little clothing can suffice most days. Bring sun-block & sun-glasses.
In wet weather(eg. steady rain, sleet or wet snow), clothing should consist of a rain-proof jacket & pants, eg. waterproof overpants. Jeans are worst - they absorb too much water too readily. In very cold/windy weather, gloves, hat/beanie and thermal underwear are essential. Weather on the mountain may be worse than in Melbourne - so be prepared.
For a comfortable journey home, or dining out later, a change of clothing (perhaps everything!) and towel - left in your car - is good insurance. Changing rooms, toilets, and snack food are available at Gerraty’s (Lake Mountain) and at Windy Corner (Falls Creek).