This is one of the most detested consumer products anywhere. The disposable plastic bag has a vile reputation — much of it well-deserved — as a wasteful use of resources and a huge source of litter that isn’t just ugly, it’s dangerous to sea creatures and wildlife.
It also comes in damn handy. You can stuff a couple of these puppies inside a bike jersey to block cold wind, or wear them over your socks to keep your toes from freezing. (Don’t forget to trim away the excess material that sticks out of your shoe, lest you blur the lines between frugality and homelessness.)
But my favorite use for these evil little things is moisture protection for my camera. Cold temperatures cause camera batteries to barely function. Often, they’ll completely fail to work until they warm up again. The best solution I have found is to carry my camera against my body to keep it warm. But that subjects the camera to excessive moisture from body heat and sweat. On top of possibly damaging sensitive electronics, this causes the lens to fog up when it is moved from a warm, moist pocket into cold air.
I need a way to keep my camera dry but accessible for quick shots. Discarded grocery bags are perfect. I drop my camera in the bag, roll the bag up around the camera and then stuff it in a jersey pocket under my jacket. As long as my clothing layers allow reasonable access to my inner pocket, I can grab the bag, let it quickly unroll, then snatch out the camera and turn it on.
Once I’m done, it’s only a matter of quickly wrapping the camera again, then stuffing it in my pocket and riding away. Even if I keep it out too long in sub-zero cold and the battery is dying, it will usually be warmed up and ready to go for at least a couple of shots at the next stop.
Green groups encourage us to “reduce, reuse, recycle.” This is one nasty, disposable plastic thing that can be reused in several ways by cyclists, and it's free.