Gift cards are always appreciated by guests. These can be made in any amount - depending what you want to spend on the prize. You could make it to a movie theater and include an amount that would take care of concessions. Or some places have dinner and movie...add some popcorn.
I never just have one game so I tend to keep my prizes on the smaller size. I've done $5 gift cards to Starbucks, Dunkin donuts, and 5-$1 scratch off lottery tickets. Everyone really likes the lottery tickets!