I think the popcorn bar idea is cute, and I like the movie trivia idea (maybe do kids movie trivia in keeping with the general theme of it being a baby shower) As for the movie, my first thought is that it would be distracting. But, pictures on a slide show are always cute. Love that idea too. Games - don't even worry about it. I've been to showers with and without games and I NEVER miss not playing games. In fact, no games at my own shower and it did not seem like we were missing anything.
My main question, though, is have you asked SIL what she would be comfortable with? If she doesn't like to be the center of attention, it can be hard, but if she agreed to a shower, she must get that she will be the center of attention, right? It's unavoidable.