Don't count on cooking much major food on a bonfire. You really can't cook in big flames like that -- you need a low coal fire and that takes a while to burn down and requires a lot of hassle. You could wrap corn on the cob and potatoes in foil and bury them in the coals and ashes under the fire but that takes a long time and stuff tends to burn unless someone is paying close attention. Get marshmallows, hershey bars and graham crackers to make SomeMores (be sure to get sticks or grill forks to stick the mallows on). Make some GORP (trail mix) with peanuts, M & M's and raisins for munching. You could get a couple of Hibachi grills and make shish-ka-bobs (shrimp, pineapple, cherry tomatoes, onions and green pepper chunks on skewers.) Freeze-dried ice cream (you can get it at a camping supply store) is usually a hit.
I doubt you will need many games for the evening. If everyone has been surfing and swimming all day they will be pretty tired around the campfire and relaxing with girl talk.
Can you rent kayaks too? They are fun for people who can't surf.
And for favors and decor, Oriental Trading company has great cheap stuff, like a dozen rubber duckies dressed in camping outfits for $5.99. You should get a bunch of lightsticks and the glow bracelets too -- always fun for night parties. They have cheap fanny packs, too. Why not get one for each guest and fill it with "camping" items like a cotton bandana, a "camper" ducky, a clip-on compass, some lightsticks, flavored chapstick, granola bars and a small flashlight?
http://www.orientaltrading.com/ui/search/processRequest.do?Ntt=camping&x=14&y=11&requestURI=searchMain&Ntk=all&Ntx=mode%2Bmatchallpartial&N=0