Really really REALLY cheap Sweet Sixteen/Going Away Party?

I'm turning 16 in December and my family has very little money to celebrate. On top of that, I'm moving to Argentina a few days before my birthday. Before I move i'm having a Sweet Sixteen/Farewell Party to celebrate everything. I live in a small town in central NJ about 30 minutes from NYC, and I have no idea what to do for the celebration. I'm only having my 4 closest friends , but I can't think of anything to do that would be really memorable. I know I'm doing a sleepover with the girls after whatever we do but i have no idea what to DO. I can only think of taking the train into the city or doing a mall scavenger hunt, but the latter doesn't really thrill me. Please help! Thanks!