If you're doing the assignment I'm thinking of (due in 5pm today), this advice is a bit late, but meh.
There's no authority for 'handshakes' per se, but in Howard Smith & Co Ltd v Varawa[1] Griffith CJ talked about 'subsequent conduct' and how the existence of a contract can be inferred by it. It is referred to/affirmed in B Seppelt & Sons Ltd v Commissioner for Main Roads.[2] It was the closest thing I could find to it.
[1] (1907) 5 CLR 68, 77
[2] (1975) 1 BPR 9147, 9155 (Mahoney JA)