What are some fun things to do at a 15th birthday party? There are both girls and boys attending.?

There are about 17 of us, and i have no idea what we can do!
my friend says its gonna be boring, so i have to prove her wrong! its on sunday, but i dont have any idaes yet.
please help!
Update: what games should we play?
ive got food and drinks organised, and music. but what activities and games? :S
thanks for your help!
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