A sanga is just slang for a sandwich. When we say sandwich we mean two slices of bread with filling in between.
That yobbo doesn't know what he's talking abot UG. Sanga is an integral part of the language we use to confound the likes of you yanks. We'd be lost without it. Besides, ask any fair dinkum aussie if they want a sanga and they'll know what you mean. If the rest of you don't understand, then that's ok. We don't really care.
(which is obviously a lie because I just gave you and explanation)