Do you have a basement? If not, if you think the tornado is really going to hit, take shelter somewhere in the middle of the house in a small room, if possible. A closet would be good.
A flash light is a good idea.
I seriously doubt you’d need to stock up on food and water. It’s not like they won’t find you pretty quickly. Tornadoes don’t last very long.
Also, you’re under a “watch” which really doesn’t mean much. If you come under a warning, get ready to run. I always make sure my camera and photograph books and CDs are by the cellar door if I think there is going to be a tornado. I also leave my shoes on (which I don’t normally do) and make sure my cell phone is on me.