Halloween!!

Hey ladies! So I'm 14, and I have no idea what to wear to our annual school Halloween party this year! You're supposed to dress up just like you would if you were going trick or treating and since I make all of my costumes I have to decide on a costume early. :) I'm not into blood and guts, or horror, so I'm having a hard time coming up with an age appropriate Halloween costume that will be fun to wear! Some of the things I like are Star Wars, Star Trek, Harry Potter, Alice in Wonderland, etc. (of course you're not confined to picking things from those fandoms) Do you guys have any suggestions? I really need some advice!!