Indeed, you used to see it (perhaps you still do) in comics and cartoons written on the bags of people escaping with ill gotten gains. I've also used the word swag to mean the stuff collected for free from someone wish to promote something. But it didn't mean anything to me when all capitalised. YOLO capitalised or not through, still remains meaningless to me.Swag is actually a really old word: "Slang originating in the early 1800s for stolen goods or booty"