18th birthday ideas????/?

So im 17year old girl and im turning 18 in december and even though its august i wanted to get a head start on all my planning...Im having 10-15 guests and my budget is very small. My guests for my party will be 17 and 18 so i want to make sure that all my guests can partake in all of the activities...there will be both boys and girls.. Please help with any ideas or personal experience with 18th birthday