It may seem odd but coupling your camera to a pair of sunglasses could improve your photographs.
In this modern, digital camera era, most camera lens filters are redundant. With film one used filters to correct for the colour of the light, for example a pale blue filter would compensate for warm tungsten lighting. In black and white photography a red filter would darkened grass, a yellow would darken sky etc. Now colour casts are easily corrected in software and B&W effects are achieved by selecting differing amounts of the red, green and blue channels from the sensor before merging them into a B&W image.
One type of filter that cannot be simulated in software is a polarising filter. When used on a camera it reduces reflections and this makes objects appear more saturated in colour. (If you ever want a photo for Autotrader, photograph your car through a polarising filter.) The blue in the sky is also reflected light from the sun. The reason it's blue is because the shorter wavelengths of light are more easily reflected by dust and water droplets in the atmosphere. In other words because there is less red reflected light it appears blue.
Polarising filters are exactly what you find in some types of sunglasses, the ones that claim to reduce glare, and while you could hold a pair of sunglasses in front of your camera lens polarising filters are generally cheaper and work even better. Check out the SRB or the Premier Ink websites, last time I looked, most sizes were less than £20.
These two pictures of Lantic Bay in Cornwall were taken within seconds of each other. It is easy to see the difference and how more saturated the filtered one looks.
You might think why not have a polariser on the camera all the time. The reason you don't is because they also reduce the amount of light entering the lens. In photographic terms 2 stops or put more simply, your shutter speed will need to be be 4 times longer for the same exposure. Not a problem on a bright sunny day but at other times it could mean a lost image.
So what about smart phones? You can can get filter holders that clip on but I have not had chance to try them yet. I have tried a pair of sunglasses but it wasn't very successful. I'm not certain but I think the small dimensions of the sensor on a phone mean that the polariser is less effective.
One final thought, with spring upon us, it's a good time to photograph bluebells and other woodland flowers. The reflected light from the flowers and leaves tends to be very polarised and using a filter can give much more saturated colours.
Sources of filters: http://srb-photographic.co.uk ; http://www.premier-ink.co.uk