DIY Camera Poncho (Rain Cover)

I don't know how many times I can annoyingly remind you that I'm heading to Iceland in less than a month, but I'm doing it again. The main point I've read again and again regarding Iceland's weather is that it's completely unpredictable. I've also read that the locals say that if you don't like the weather, you can just wait fifteen minutes. Because there is a v. good chance that we'll be caught