Getting to Churchill, Canada is not cheap. When I took the trip a few years ago, I was taking an on-line course at the time and contacted my on-line photography instructor (Jim Zuckerman) to get an idea of what to pack and how best to shoot in flat light. The following information is from Jim's suggestions and what I learned when I got there.
When shooting the bears of Churchill pack long fast glass with you (rent if needed) as well as an extra camera body with a wide angle lens. If you can get hold of one of the big lens (they can be rented locallly or on line) a 600 mm lens with a f2.8 or f4 is great. If you can?t afford to lease a lens, the Canon 70-200 f 2.8 and Canon 100-400 mm f5.6 with a 1.4x teleconverter also works. The teleconverter does knock off a stop of light, so you have to take that into consideration.
The lighting is flat and low so expect to bump your ISO up to accommodate and over ride any movement in the tundra buggy. Also set your camera to fire in bursts to make sure you end up with at least one image in your group that is in focus. Use the autofocus to obtain original focus on the eyes and adjust as needed. The action can be fast, with bears or fox on both side of the tundra buggy and the bears can be far away and then all of a sudden right under you (this is where the wide angle on the extra camera body comes in).
Take multiple batteries with you as batteries don?t fare well in the cold. I was mostly using my Canon 1D M3 and the weather proofing was such that the batteries had no problem at all (I would assume that other weather proof cameras would be similar). If your camera is not weather proof (such as my second camera body- the Canon 50D) bring heating packs and tape them under the camera by the battery.
If your camera isn?t weather proof, bring some type of protection for it (a cover). At one point during a snow storm, my M3 was so covered in snow and ice that the controls were frozen. It took some time inside the tundra buggy to thaw it out to where it was usable.
Bring lots of CF cards (or what ever cards your camera takes). I took over 5000 images in 5 days. I downloaded them all onto the Epson 6000, but even two of those devices were not enough for this trip (one to download to the 2nd as a back up). I had 15 4-8 GB cards and it worked out perfectly.
One of my biggest worries is packing all this gear. The rented lens can be shipped to your destination and then shipped back. It takes a suitcase of its own. I finally settled on Think Tank?s Small roller. It fits perfectly in the smaller planes that go up to Churchill and the thought of ever having to check my camera gear sends waves of panic through me. I have talked to too many photographers that have ended up with part or all of their gear stolen in their checked luggage. One photographer had his whole Pelican case emptied (they left the Pelican case).
Bring a monopod!!! This is critical. I use a monopod by Monostat that has a large rubber rotating foot that allows for excellent stability and it rotates around the axis of this head (important when the action is fast). You can rest your lens on the glass windows of the tundra buggy, but part of my time was spent off the back of the tundra buggy on the observation deck. I also found the monopod to be much more stable than the windows, as the windows picked up the vibration from the tundra buggy much more than the Monostat.
Other things to pack: battery chargers, cleaning supplies for lenses, a lens blower, many people on the trip with us had computers and processed their images at the end of the day, extra lens caps (I found one of my Canon caps on a Nikon lens in the tundra buggy- they get picked up accidently), a circular polarizer, a 2 stop graduated ND (the kind that is rectangular and that you hold on your camera), a cleaning cloth to wipe your camera down after bad weather, hoods for all your lenses and plenty of those little heating packs that you crush for heat.
I will be returning to Churchill in 2010 and am really looking forward to it. Being surrounded by Polar bears in on the tundra buggies and seeing these beautiful animals in the wild gives me goose bumps and the biggest rush I have ever had with photography.