Surprise!
People enjoy the unexpected (e.g., place setting treats, special guest, personalized items, etc.).
Consider alternative seating arrangements. Set up conversation areas around the room, particularly around displays if you have them. Allow seating options (at table, chairs in a circle, etc.). Use “fun” chairs … blow up recliners for a game watch, comfy couches for an informal talk.
Prize giveaways are always a big hit. You could encourage people to bring a friend to win a prize.
Be creative about special recognition (e.g., best UW story).