Stuff I've gotten from conferences I've attended over the last few years (in no particular order)
- Learned stuff from good quality presenters
- Learned how to do good presentation using PowerPoint, instead of usual Death By PPT (the speakers/experts at the conferences I've gone to have been very good both technically and as presenters)
- Picked up a few shiny things from trade stands alongside the main conference
- Free beer and food at post conference networking sessions
- Chance to travel to new places, and try to fit in a bit of exploration
I don't think you'll ever go to a conference where every last minute is of value to you, but there should be some things that you can take away and get benefit from after the conference. The big challenge is trying to express that with some form of tangibleness so that you can persuade your boss to pay for your fees, travel, accommodation, etc.