When I left for my Alaska trip, I was packing on the end of a 90+ hour work week and was still actively fighting against a DDOS attack on the site as I was going out the door. With major distractions, I left without a key piece of kit that I expected to need on this trip – my Think Tank Photo Hydrophobia 300-600 v2.0 rain cover. When I remembered what I had forgotten, it was too late to recover from my mistake.
As it turned out, I was shooting with my Canon 600mm f/4L IS II Lens on a Canon EOS 5Ds R in light rain about 50% of the time I was in Katmai National Park. While this lens and lens combo is weather sealed, I don't like to test the limits of this sealing.
What saved me? Minimally, from anxiety? A simple garbage bag. Having needed to use this backup plan before, I knew what to do. Place the makeshift rain cover (I usually carry at least two in my larger cases) over the camera and lens. Then tear a small hole in the bag, with the opening just large enough to tightly stretch over the lens hood. The plastic stretched around the hole holds the bag tightly to the lens hood, providing a seal between the gear and the makeshift rain cover.
A hole can also be made for the viewfinder, but I often use the bag's normal opening when shooting. My ball hat brim provides some protection for the exposed back of the camera and I pull the bag completely over the camera when not actively shooting.
This solution is not nearly as elegant as the TTP rain cover. The one problem with this setup is that wind can swiftly blow the bag off of the camera, generally turning it inside out and into a flag blowing from the snug-fitting tear/cut hole hold holding onto the lens. Wrapping some tape (carry a small, perhaps self-made, roll of gaffer tape) around the back of the lens can be enough. Other securing options abound, including the use of ball bungies.
Forget your garbage bags? Garbage bags are ubiquitous; they can be found at most household supply, grocery and camp stores. Your hotel can likely give you one if there isn’t a good one to be found in your room. If your hotel happens to provide shower caps, that is another rain cover option.
Garbage bags have many uses beyond camera and lens rain protection. Use them as a drop cloth/ground matt to keep you and/or your gear clean and dry. You can even put your camera case/backpack in a bag. Use a garbage bag as a makeshift raincoat for yourself (important: allow for fresh air to prevent suffocation). You can of course use the bags for their namesake purpose. Carry a load of trash out of the location you are shooting in.
Choose your bag size and its duty-level based on your need. While a super telephoto lens works great with a full-size garbage bag, smaller lenses work better with a kitchen-sized garbage bag or smaller. When used as a ground cloth, my preference is for very heavyweight contractor bags, though I find lighter weight garbage bags easier to work with as a camera rain cover. I often have various size and material weight selections at my "disposal."
While it is your choice, I highly recommend "unscented" bags. :)
Garbage bag are cheap, readily available and incredibly useful. Put some garbage bags in all of your camera bags now, before you forget. And, add this useful accessory to your packing lists.