One technique we've evolved is setting up a 'prize desk' that controls and secures all raffle prizes, book, etc.
You need at least one person at the table at all times, so you have to have a backup for breaks. Consider co-locating it with registration.
Having prizes visible is a great way to encourage attendees to stay to end of day.
Pize winners bring a raffle ticket to the desk and then claim their prize. For some tickets they may be 'you won a book' and they get to pick from available inventory, in other cases it may be a for a specific item. This method allows the prize drawing at the end of the day to proceed quic