Offer volunteers and staff assisting on live events a personal letter thanking them and acknowledging the role and tasks undertaken which can then be included in their portfolio. For regular volunteers and casual staff make it clear that you are happy to give a reference. If they make a good impression they could even be considered for any permanent posts that come up within your organisation.

Communicate
One difficulty of working with event staff and volunteers is that you don't have much time to chat and get to know them during the most pressurised times, such as for the live events. Strive to value every member of your team and take a genuine interest in them as a person when you can. Ideally this would have been possible at the interview stage but also ensure staff are briefed in person before the event start time and informed who to contact if they are unsure of anything at any point. Try to talk to them and find out what motivates them and makes them tick.
Volunteers and casual staff need to feel they are included and part of the team and the bigger picture. Ensure they are introduced to everyone they will have contact with/ work with, including both casual and permanent staff.

Think About Logistics
Try to choose staff based on practicalities or tailor the role to suit their circumstances. If a member of the staff can't drive, lives far outside of the city and you need them on site by 5 in the morning it may be virtually impossible for them to get there by public transport. Unless you can pay for their accommodation onsite or facilitate a car-share you should question if they are the right person for that specific role or if you are just inviting problems.
Keep a list of staff mobile numbers in hand or programmed into your mobile so you can make contact quickly as required.

Brief Staff Fully
It is important to brief staff so they understand their role and what is expected of them. This will also help to take some of the anxiety away for them. It can be quite daunting being part of a large event and not everyone in the events industry is confident and outgoing, particularly if they are just starting out.

Value Their Feedback
Let staff and volunteers know that you truly value their thoughts and ask for and listen closely to their feedback and suggestions. Your team will often hear opinions or suggestions from guests and attendees which are vital honest feedback that you are not aware of and may inspire ways to do things better and differently in future.

Recognition and Praise
Event days are often long and hard. Thank the team and feedback praise from the client, attendees and so forth. Try to ensure staff leave on a high and feel proud of their contribution!