Simplest solution: We can allow presenters to upload stuff here. That will give them full add/edit/delete on this page. Should be fine, but not totally secure.
Create some kind of anonymous upload dropbox somehow and have someone curating the materials here for download. Some technical challenges and some labor involved.
Create pages here for each session. Give the present edit access to their own page. Some different work required, but probably leads to a nice result. Might be worth doing. Maybe some way to automate this? See an example of this here: Presentations 2