OK, i already know what you're saying, why buy what i can make out of a shopping bag? Easy: This is already stoopid cheap, and it works better, and won't make you look like an amateur.
Here it is: amazon.com/dp/B000PTFDYO/?tag=mhlocal-20
Want something less disposable? amazon.com/dp/B004AH10K8/?tag=mhlocal-20
How many times have you been caught in the rain? If the answer is even 1, you should buy a pack of these.
I've been there, salvaging a grocery bag to cover my camera. Hey it works! But it's certainly not ideal. Enter the rain sleeve.
It's about as basic as you can get, it's roughly shaped like an DSLR with a hand and arm attached to it. add to that a premade hole to poke your viewfinder through and a drawstring for the lens and that's it.
It's not for large cameras, i haven't tried it with a battery grip attached but i think that would be a stretch. I haven't tried getting my C100 into it because i'm quite sure it won't fit. DSLRs and small video cameras only. The arm sleeve makes it easy to get a real grip on the camera, but you might find it's perfectly easy enough to access the camears buttons through the thin plastic. Dials/rotations maybe not so much.
Pretty much useless as it's got nothing to really grip the end of the lens with. Solution? A little piece of gaffers tape to the hood of the lens, perfecto! If you're feeling frisky, put a full circle of gaff tape around it.
Is probably just the right thickness. It wont fend off a sharp object, but handles some grab and pullin' just fine. It's thin enough to give you tactile feel through it. How does it compare to a grocery bag? much thicker. Grocery bags are thin as all hell, but these sleeves are a decent amount thicker and while they don't scream high end rocket science, they do give you a sense of security for your camera in wet weather.