Hi Beth, I've been volunteering with Festaff for a few years now and I love it.
Make sure you bring your paperwork and I.D with you.
Also some good earplugs are a must if you want to get any sleep at all! I just had the foam ones the first year but since then i have got some of the silicone ones that mould into your ear. Although the vol camp sites are relatively safe, I still would keep valuables at a minimum but thats just common sense!
Try to pack as lightly as possible (I'm not good at this!) and if you are coming in a car and can fit a trolley in then get one, depending on which festival you are doing its sometimes a long walk!
If you have any specific questions I will help if I can!
Enjoy xx
Bongo Jacci