I'm not familiar with the illustration course but usually people do something related to their previous course and what they want to do in their career (having said that I studied print journalism and ended up doing a radio documentary!). A lot of people do things like a magazine, booklet, website, music video, radio doc, radio drama, promotional package for a band...
The main thing I would say is to have a client/sponsor in mind, for example you might know somebody starting a company who needs a website designed, a band that needs some promotional material designed for an album release, an organasation (charity or otherwise) that needs a booklet or something designed to highlight something. And even if you don't know anyone who needs that kind of thing done you can just make it up, you're not expected to carry out the project you pitch in the interview. Remember you're the coordinator so even if you were designing a magazine or something you could say you're going to reach out to the journalism students for the written content.
You can also be your own client, I think I heard of someone making a portfolio for their media project. Also just mind the scope isn't too big for the time you have, and show you've thought about the practicalities etc.