You might want to consider reservations for Denali and the tours in Denali (if you plan to go deep into the park). We made our bus (tour) reservations last April and we got the last seats on the tour we wanted.
Consider reservations for July 1 (Canada Day), if you are traveling through Canada on your way. Ditto for July 4 in Alaska. Remember the Kenai Penn. is the playground for many Alaskans, especially on weekends, as it is reasonably close to Anchorage. This is true with Banff National Park and Calgary in Alberta as well.
Finally, if you are using the Alaskan State Ferry for any part of your trip, I would recommend making a reservation for that as well. BTW, strongly agree with the book recommendations. One addition, if you belong to the AAA, get their tour book for Western Canada and Alaska. Enjoy your trip!