I've done it several times and all good advice above. You only need The Milepost as far as books, unless you want something specific like "Birds of NWT" or something like that. I've done it everywhere from 4 days to two months. Spare tire as mentioned, and if you're towing a trailer, have a spare hub and what you need for bearing swaps, should the need arise. And then be proficient doing bearings. I literally had a pit stop kit ready to go and could redo a bearing tool box to tool box in no time, in the dark.
Also have several friends who've done it and while I've never had a horror story, common horror stories involve radiators/coolant, head lights, transmissions, trailer hubs, flats and then freak catastrophic failure. Before my last trip, I replaced my water pump and radiator, head lights and even had my transmission rebuilt (because it had 160k on it and I was towing 5,000 lbs) before my trip. If you're towing, I recommend a simple set of air bags and an external tranny cooler. Two simple add-ons that make a huge difference towing.
As far as planning, figure out what you want to see along the way ahead of time. If there's a cool fly shop in Kamloops, plan on that before you get half way through BC and realize you're 600 miles away and on the wrong road and can't get there without back tracking. The trip can be as rugged or as comfortable as you want it to be. Have fun!! I've enjoyed the hell out of it every time I've done it.