Shooting pictures with an iPhone can be super convenient, but sometimes you want just a little extra help to get your shots just right. It isn't always practical to carry additional lenses around with you, or sometimes you are unexpectedly in a place where you could really use a good filter or two. Luckily there might be one with you already: Your sunglasses.
What, don't YOUR sunglasses look like this?
If you are in a location which is particularly bright, or you notice that the colors you're seeing behind your shades are more vibrant than what your iPhone camera is picking up, you can adjust that a little by holding your eye's lenses up to your iPhone's lenses.
For example: In the below image, I'm dealing with some serious light coming through the shades, so it's making it hard to see the other things in the photo. So I hold up my sunglasses and get a much nicer "baseline" image (which I can then take to Pixelmator or whatever else and have a better starting point).
Behold! I have Tiki Mugs. And you can see them better through a filtered lens!
As I mentioned, you can also see more color, not just manage light better. I took this shot of the same cloud both with and without that extra lens:
There's quite a difference here...this is from back when we still sort of had clouds.
So while the old saying goes "the best camera is the one you have with you," you could maybe add something about the best filters as well.