For instance, if the person is celebrating their 60th Birthday, ask guests bring a photo of themselves when they were together in college, or were co-workers, etc. Makes for great memories and lots of talking over of old times. The most romantic moment Something the birthday celebrant did to change my life Etc. etc. etc. If you're having the party in your home or at a restaurant, buffet style is the easiest way to serve food. If you are catering the meal, buffets are often less expensive than a formal sit-down affair.
Snacks are important to provide for guests to munch on until dinner is served.
Even if you've never thrown a surprise or adult birthday party for someone before, ask around for suggestions and ideas. Think back to parties you enjoyed and remember what foods were served.