First, I wanted to thank all of the Effective Altruism Global organizers and participants. I found it to be very valuable and overall well put together. There was obviously a ton of work put into it, most by conference organizers who I don't believe will get that much credit for it, and I very much commend their work.
That said, there's always a lot of room for new ideas, and I find I often get a bunch of ideas at and after these conferences. Because of the EAGx events, ideas described now may be able to be put into action somewhat soon and experimented with.
As may be expected, I recommend that people make all of their ideas be independent comments, then upvote the ideas that they think would be the most useful.
Perhaps we can have badges with QR codes that you can scan with the app on your phone to immediately add the person's contact info to your address book. Or with precise enough GPS locations (that we'll have because of the walking meeting idea) we can have an algorithm automatically determine which people you (probably) talked to during the conference based on proximity, setting, context, and length of contact. This could also be done with simpler sensors that just detect proximity.