Have cloths/ towels on hand to deal with spills. Be quick and don't disrupt the talk/performance.
 

If a glass cracks, replace the glass immediately and carefully, and then refill it.
 

If a glass shatters, event staff/student helpers should carefully redirect people around the site, sweep up the glass shards, wipe up any smaller fragments, then dispose of the shards and towel appropriately.
 

If rented drinkware is damaged, it should be discussed with the organisation rented from. They may have policies about this already in place. Seek more information from individual renters.