Having a proper agreement in place will also help you define the scope of work that is expected of you. What if the plan for the day was for a four hour event but due to various reasons the day became twice as long? What if the party goes on until the early hours of the morning but you’ve been working since 8am? Are you expected to stay for the same amount of money? Limiting the hours of work and specifically mentioning the deliverables will make your life a lot easier. If you are forced to stay longer you may now also bill the client for the extra time.