In my personal experience, a conference was never a waste, I was really lucky because I had the chance to travel a bit, to meet really smart and nice people, eat good food (not always), exchange ideas and occasionally even be interested by the topic (just kidding), I am never… (I am kidding now).
Anyway I believe to be this kind of person that in conference could be defined a “collector”…. I was really used to get crazy for collecting all the possible useless gadgets, pens, books, and of course “The Bag of the conference”!! But I am now a “Regretful collector”… I realized how many useless plastic / PVC / acrylic bags I collected…. and they are all broken… They broke just after the first or second week…. Useless plastic things made in china… And I found particularly incoherent the use of those bags in conferences dedicated to “sustainability” and “green chemistry”, considering that for 200 or 300 participants, you realease in the environment such a potential waste.
I instead particularly appreciated the initiative of 2 Universities, the University of Salerno (Italy) and the University of Freiburg (Germany), that while hosting a conference, provided to their guests, bags completely made of cotton (or some mixed fiber). These bags (miracle of modern technology) not only didn’t break, but they are still of use for shopping. If one day they should break, it will be possible to repair, and if one day I’ll decide to throw them away, I’ll not feel so guilty, after all it’s not such a waste.