Could someone help me with birthday party ideas?

I'm turning 17 soon and i wanna do something for my birthday, nothing too expensive because the present i want for my birthday costs quite a bit. There will about 6 girls plus my boyfriend and his friend, i want to do something special but not too extravagant (saving the big party for my 18th lol) any ideas? please help. Btw i live in London and so the weather is not great. Thank you in advanced :D