While entry is free to most fairs, you should check if tickets are required, plus verify times and location carefully. It is always useful to take copies of your CV along. You can usually photocopy at the fairs but queues can be long. These are usually for final year students but some employers have opportunities for placements. Presentation are designed to give you an insight into company structure, graduate opportunities and training, plus details on how and when to apply.
Smart dress is recommended, particularly for evening presentations.