As for Food and Drinks for an adult surprise party, there are so many alternatives. Are you having it catered? If not, make finger foods or have trays of food made. It all depends on what you want. But keep them simple instead of ornate. People can be picky with foods. Good selections are baked ziti or stuffed shells, salads, chicken, deli trays, cheese and crackers, hourdourves type finger foods. Make sure to have water, diet and regular soda, beer and wine if applicable. I would stay away from hard liquor... this can be a problem for guests that are driving.
Decorations... this can be fun... blow up a picture of the GOH and hang it somewhere for all to see. Have pictures of the GOH all around on display from the time they were born to recent shots.
Have a roast or This is your life theme ... have the GOH's friends, family and co-workers talk about different things that happened from the time they were kids until recent past. Share those fun and embaressing stories.
Have a few SURPRISE guests.... maybe an old friend the GOH has not seen in a long time. Have them stay in another room and at the appropriate time, have them talk from the other room and let the GOH guess who it is. Have the surprise guest give clues as to who they are.
I hope this helps, let me know if you need more
Good Luck!