Is there a village or town? You could go into town for a meal or window shopping. At the beach... Beach Volleyball, badminton, throwing frisbees, making sand castles, go on a scavenger hunt ( a certain type/size/color of shell, sea glass, bird feather, drift wood that looks like an animal,- etc. I'm sure you could come up with a bunch of stuff you can find on a beach).

Do you have any board or card games?

I would just plan to have some activities to break up the sunbathing so that folk's don't get bored.

Not sure how much it would be - rent jet skis for a few hours :)

My birthday is in two weeks and I want to have a party in a few weeks with about 10 of my girl friends at my family's beach condo, itd be an over night but I dont know much to do except we'd get there around 9pm and settle in, the maybe watch a movie and go night swimming or walking on the beach. Then just a beach day the next day but does anyone have any ideas of anything else to do that wouldn't cost much? Besides the typical like oh a photo booth, go swimming and decorate cupcakes, makeovers or painting nails! Lol all of us are 15-17 yrs old :)