What could you do if you went back in time?

I have thought about this before and it makes me feel pretty lame. If you were to be zapped back in time. Lets say to the early days of Egypt. What could you do or make with your current knowledge that would show you were from the future. Or to show you had a great knowledge. Besides knowing facts of things to happen. I wouldnt even know where to start to create a light bulb or raido or something. I feel like if I went back in time I would be hopeless to show anyone great things from my time 2011. What do you all think? What would you do to wow them! Serious