16th Birthday Ideas?

I'm going to be turning 16 in March and I want to start planning as soon as possible. I'm not sure whether to spend a day out shopping just with my close friends or have a party. I don't want a house party because I don't want my house trashed! But at the same time I want to do something with girl mates and boys, too.

So you see my problem. My mum doesn't want to send too much money probably about £100 max. If invite boy and girl mates then there would be about 12-20 max of us. I want something for us all to do and that we wouldn't get bored either.
I'd be very grateful for any suggestions.

By lozza.x