In popular culture, the term swag now usually refers to promotional items or gifts that are given away by companies or organizations. It can also simply be used as a slang term for undesirable items in general.
In Britain it can mean items acquired informally or actually stolen. In cartoons, burglars are traditionally depicted with their faces masked, with a hooped top and a large sack over their shoulder clearly marked "swag".
Backronyms of the word include "Some Worthless Advertising Gimmick", "Scientific Wild Ass Guess", "Stuff We All Get", "Stolen Without A Gun" (police report jargon), and "Stuff We Ain't Got". One current interpretation of the word is "So What, Another Giveaway?".