I'm stuck on thinking of a third body paragraph for an essay, the topic saying that Australian identity is strongly related to informal language usage. I've already talked about it being a medium of expression and it reducing social distance and indicating the easy-going nature of Australians but I can't for the life of me think of the last one. Could someone help me out?
This really all depends on your contention. You want it to be slightly more complex than a basic agreement with the prompt, otherwise you'll struggle to hit the higher marks.
I think I'd have my third and final paragraph about the interplay between formal settings (context) and informal Aussie lingo. This can be seen with something as simple as Scott Morrison's speech to the media today in relation to the Coronavirus, using the phrase 'Pacific Family', being idiomatic as they're technically not family, but it exemplifies the Australian value of mateship. Additionally, I'm sure you could find many other examples of those in formal positions (eg. businesspeople, politicians, white collar workers etc.) using Australian slang at various points. This is more subtle than the language just exemplifying the 'easy-going nature of Australians', but that it actually forms as a part of everyday Australian communication, even in more typically formal contexts.
You could also centre that 3rd paragraph around an 'appeal to the Australian public' (ie. they're laypeople, and due to a degree of tall poppy syndrome, they don't like people sounding better than them).