I just had my son's birthday party. We had a Disney Cars theme party. The kids loved Pin a Tire on the Car (a takeoff from pin the tail on the donkey). They also enjoyed musical chairs - the older kids controlled the chairs and music. Also, I made a treasure hunt for the kids. I placed clues around the house that they had to find in order (i.e. You watch the movie cars on this - then the kids would find the next clue at the TV). In the end, there was a treat bag for each child.
One idea that I didn't end up doing, but I thought was cute, was to make a large card (poster size) such as a large Mickey Mouse. You could have the kids decorate the card and write birthday wishes on it, and then you have an activity and a keepsake too.
I hope your party is a success!