Depending on the definition, nothing.
Over the years I have heard the use of SWAG in varying contexts. Many years ago I worked in the tech field and one of the programmers got a kick out of answering your question with a wide smarty pants grin. He was waiting for you to ask him “What kind of answer is that?” The common answer was WAG for “wild ass guess” but when he was feeling particular ornery, it was SWAG for “sophisticated wild ass guess” which meant there was a little more data to back up the WAG.
It is used to describe the way a person walks or moves as in “swagger” as well as “swag.” It is also, as described in the dictionary, a curtain or piece of fabric which hangs in a drooping curve.
Today we hear SWAG when referring to free stuff (or loot) given out at events. Attendees are given free stuff promoting a product, artist, company, etc.
In the 1960’s it was used as a reference to promotional products and this is the use, I think of today.
Swag bags often have a combination of items. Some are imprinted with the sponsor’s logo. These items may be small items like bands, tshirts, pens, pads, or battery operated fans. This list can go on forever. Upscale bags may contain watches, jewelry, travel, post cosmetic surgery supplies or fitness products.
Other items may be tied to the release of a new product like cosmetics, cell phones, food stuff or teams. A company may use SWAG to get the word out about a new warehouse location, division or change of address.
Maybe you have a small sporting goods store or bait shop. You don’t have the resources of the big guy but you would like to have your information out there. Maybe you want to offer a free gift with purchase. You can have your information imprinted on fishing lures, bobbers and get custom packaging as well.
If you have a bait shop or sporting goods store, you wouldn’t want a SWAG bag like the one shown above, but there are other bag options out there for just this purpose. Maybe a kraft style paper bag or and insulated lunch bag.