Halloween/GenCon

Every year my brother has a Halloween party. This year, it's themed. GenCon themed. Scifi/comic book/fantasy/video game/cartoon themed. I have NO clue how to dress. I've been running some ideas through my head, but the ones I THOUGHT would be good, well, they're super skinny and wear tight or little to no clothes. Not for me. I'm thinking Indiana Jones, Elsa from The Last Crusade, Moiraine Damodred, Phedre no Delaunay...but still, not a clue. If any of you have any ideas, and I mean ANY ideas, let me know quick because I'm doing my shopping tonight and tomorrow. I'm excited about it either way.