Fast food is not your only option. If you're willing to work outside of retail there should be plenty of people looking for labour, office or other odd jobs advertised on forgotten places such as school/uni bulletin boards, perth.gumtree.com.au or the community paper. They might not give you work every day of your summer but its still work.
Unfortunately if you don't have a car it can make it difficult to get a job. I remember the pain.