In 2020, several publishers gave an ebook license or discount code for all attendees. It might be better to request more of those kinds of rewards from publishers and do fewer individuals prizes.
Book Raffle =
It would be nice to hit up some publishers for books to raffle off at the conference. If you've got ideas add them below under the name of the publisher. Most tech publishers have user group coordinators that are more than happy to make donations available.