Green’s Dictionary of Slang

(Aus./US) a sandwich.

1972		A. Chipper Aussie Swearers Guide 43: Sammo (or Sango) Merchant: Hearty eater of sammos or sangos (sandwiches).
1988		Canberra Times (ACT) 29 Mar. 23/5: After they had demolished three plates of sammos and as many cups of tea they entertained with stories of their travels.
1990		Canberra Times (ACT) 9 Jan. 13: Lunch was beaut – soup and sammos on the terrace.
1995		Canberra Times (ACT) 4 May 2/7: Some how Ms Owens couldn’t quite come at the rest of her ham and-cheese sammo.