I've been to meetings where they had a student volunteer positioned in each room:
- they swapped out the name cards where the speakers will sit
- they replaced the water bottles at the speaker table with ones stashed behind the podium
- they helped out with AV issues, or called for expert help.
- they kept a count of how many people were attending each talk in the session.
This gave them a chance to attend talks, albiet with some minor distractions as they did so.
They were wearing brightly colored shirts labeling them as volunteers, so people also knew who could either answer their questions or point them in the right direction of someone who could.
At other conferences (eg, AGU with thousands of posters displayed per day), we'll often assign students as the session chair for posters:
- Grab a supply of pins from the main desk, and the signs for when you'll be at your poster
- Help people find their poster location (look it up online or from the printed program)
- Help people hang their posters (or at least get the top two corners pinned)
- Record any posters that were no-shows.