The big item I forgot was a water filter. There is river water that can be used, but I generally prefer to filter any natural source prior to drinking. There were no other water sources.
On the James Bay Road, the mosquitoes were thick. I had jammed screening into the window moldings so I was able to keep the windows open, but the whine of thousands of mosquitoes outside of the vehicle was a bit maddening. It was hot when I was there so I definitely needed open windows. I did a few short hikes but kept moving fast to try to avoid the cloud that was following me.
There were roadside pulloffs that looked like they had been used during construction, and there were free campgrounds along the way with donation boxes. There was almost no traffic, so I was generally happy to hear a car every hour or two, just to know there was someone else out there. There are also powerline roads, logging roads and various two tracks that one can pull off the main road and camp. I'm not sure of the legality of camping but that far into the bush I don't think anyone cares. There were no people anywhere for hundreds of km's. Quite a few of the campsites are at river crossings and they were quite scenic. I would recommend moving slow and boondocking for longer periods of time along the way, just bring all the food you need and bring a screen tent.
I would like to return, ideally during cooler weather when there are no bugs. I would like to go to the villages on James Bay and meet some people, on my trip I was alone and did not see anyone out and about when I was in the villages. So I didn't talk to anyone in the Cree villages, I think they were avoiding the bugs. In Radisson, I was embarrassed that I did not even know how to say the basics in French, please, thank you, good morning, etc. Next time I would take a cheat sheet with the basic phrases of French out of courtesy. I started talking with some people and was surprised that their English was not that good, and they were trying there best to be friendly and talk to me.
I would also like to go to one of the Northern stores, that are the current versions of the Hudson Bay Company stores, and see what they have. It would be cool to go out with a freighter canoe on to James Bay (part of Hudson Bay), but I was on a budget so I did not try to do that.
I had no problems on the James Bay Road but if my vehicle had a mechanical problem, I would expect it would take a lot of time and money to fix it. I am sure there are people who can fix things at the villages, but they are about 100 km apart or more.
Gas prices are high, so I think the best strategy is to stop frequently and camp, and explore areas by foot or bicycle. I could see spending two weeks on the James Bay Road. After the trip, I was pretty happy to get to Rouyn Noranda, which is sort of the end of civilization before the James Bay Road starts, and get some junk food after my trip.
You need enough cash to pay for things, credit cards don't (or didn't) work north of Sudbury. They may work now but I would carry enough cash for the whole trip. You need to fill up your tank at the gas stations at Radisson, Relay Routier and Matagami. If you do that, you should be OK with fuel. There is fuel at the villages on the bay as well.
The rivers are the main places of interest, so a kayak might be useful. You have to be somewhat conservative because there is no one out there to help you. It would be pretty cool to kayak in the small bays and island areas near shore in James Bay. I am not sure what kind of sea monsters might be out there, seals, whales, walrus, polar bear or ???