For my tenth birthday party, I remember doing a sleepover party. I had all my friends come over around four or so, so we could begin kind of early. We played Twister and for dinner we ate food from a take out resturant (I think it was like Subway or something). We listened to music and danced. We had an ice cream cake from a store called Willies (it was SOOOOO good!!!!). Then we opened gifts. One of my presents was silly string, so we went out front and sprayed my two big trees with silly string!! Then (in honor of September 11th) we made signs. When we stood in a row, and all in order, the signs read: Honk If You Love America. We got SO many beeps from passing cars! One guy didn't stop beeping! It was SO funny! When we made it to 50 beeps we went inside to listen to music some more. Then we ran around outside! By then it was 10:00 and we were getting kind of tired so we rolled out our sleeping bags (which took about half an hour 'cause we kept changing our minds about how to set them up). Then we watched movies and pigged out on junk food.
I REALLY hopes this help you out. P.S If ANYONE has ANY ideas for a 13th sleepover party I would REALLY use them!