Special events by their very nature invite large groups into designated areas, which require that their basic needs be met.
Based upon the estimated crowd, portable toilets or rest rooms should be conveniently located. The same is true with refuse containers. They not only need to be conveniently located, but also regularly serviced to make sure that they are not over taxed or filled beyond capacity.
After the event is over the site of the event should be restored to the same condition as was evident, prior to the event. Similar to good hiking and camping protocols, if things are brought in by the planner or spectators, then they should be taken out again. The positive influence of a well-run event lingers well after, but the debris or other reminders should be long gone as the site of the event is restored to the original condition.