This term arose out of the military from WWII, generally attributed to field artillery officers who asked their spotters to "swag it" when asked for an approximation of how to adjust. This expanded to all of the military, and then entered use by the rest of the world. "Swag" with this meaning has been around for nearly 70 years and is still used widely in the military and business world to this day.
2. Something given out to everyone within a specific group of people, be it the PTA, or all the attendants of a seminar, or even all the people visiting a certain booth at a convention. Also items within a bag of the same name as in "Swag bag"
3. Very recently (late 2000s, early 2010s), coming out of the ghetto, a shortening of the word swagger, used in place of extreme confidence/cocky attitude. Also see tude
"Can't tell you precisely what revenues were last year, but I could swag it at $10 million or so."
2. "O! M! G! Did you see all the swag we're getting this year Becky!?! And just for going to cheerleader camp!?!"
3. "Dat's right mutha-fucka, she's wit me, cuz I got swag!"