Your camera roll makes a very handy To Do list. When you're out of a food item, take a photo of the package before pitching it. When you go to the store browse your camera roll thumbnails for what you need and delete what you put in your cart. This is especially useful for things like ink jet cartridges that you never can remember the number of. The iPhone camera can be used at about a foot away, so you can accurately capture readable serial and model numbers.
