What to do for my sweet sixteen?!

my birthdays on a saturday so im thinking about having people over on friday and going for a meal and them to sleep over in a tent afterwards.. but i dont know what to actually do on saturday which is my birthday.. i cant think of places to go ? so i was just wondering if anyone has any ideas.. coz i live in the country (Somerset) and its really not sunny so is there anything we can do but not travel very far ? and something not that expensive? thanks for your time :) x