I wonder when and why conferences picked up the habit of giving out conference bags to attendees.
For the why part: One reason is to make registration at the conference as smooth as possible. Imagine the first morning of a conference and all the attendees at the registration desk lining up and for each and every participant the guy at the desk hands over the program, the book of abstracts, the badge, the ticket for the conference dinner, the ticket for the prebooked tour (if there is any), the receipt of attendance, the receipt of payment, the complimentary notebook and pen and, of course, the stuff from sponsors. Takes much longer than pre-packed bags. (And even with all things pre-packed, there are always queues during the rush hour.
As for the when part, I have no idea. But if you have ever sat at a conference desk you'll agree that it must have been no later than the first time one guy organized a conference with more than 100 people for the second time.
For the at least the first few conferences I attended, the bags had a clear function.
The attendee packet included a lot of paper, often more than could be tucked into whatever bag one was carrying. There could be several separate documents, such as a schedule grid and the printed proceedings. Carrying them around loose was inconvenient and risked losing some.
Providing a bag big enough for the attendee packet contents was a thoughtful gesture.
The bag gives attendees a place to store all the advertising and marketing materials (such as coffee cups and notepads stamped with the company's logo) that are handed out by vendors at conferences vying for attention.
These marketing materials are often referred to as swag, and the bag for carrying all of it is called a swag bag.
Having the conference hand them out to everyone at the entrance saves vendors from the cost and effort of having to each make their own bags to hand out to attendees.
The bag also makes it more likely you will take the stack of promotional items home with you, rather than discarding them due to having your hands constantly full of loose items.
Ah! I was just at an expo where they only gave out plastic bags (which is super rare these days). I can tell you what I did with it.
I looked inside it, quickly flipped through some of the junk marketing materials, found a little toy, pocketed the toy, and then I immediately placed the bag still full of junk marketing materials in a large box where dozens of attendees had already left their plastic bag.
If it had been a tote bag, I definitely wouldn't have thrown it away. Usually with a tote bag, I wait until I am sitting down somewhere before I start sifting through its content. And I only start throwing away some of its content if I happen to be sitting next to a trash can, or what usually ends up happening is that I bring the tote bag back home, and I do the triage there.