The lock was necessary because I have no secure storage for the bike (Burgmann College was not enthusiastic about the idea of stashing it in my room) and an unlocked bike would be pretty much fair game for some (probably drunken) random in a hurry.
You will also need a skid-lid.
Quoting SJH on the ride itself:
The ride is open to all delegates at the conference, meet at 10am in front of the Manning Clarke Centre with a bike, we plan to leave by 10:30am and ride for approximately 2 hours. There are some bike hire places in Canberra if you are unable to arrange a bike, further information is available at the registration desk during the conference.