Great advice from all the previous replies. I agree with everyone who said to be flexible. If we had been on a strict schedule we would have missed so much.
We made the trip from Georgia in 2013. We left Georgia in mid May and got back home September 1. We would have left earlier but we were waiting for a grand baby to be born!
There are two main things I would do different:
1. Spend less time getting to Alaska and more time in Alaska.
2. Spend more nights in State and Provincial Parks and less time in commercial campgrounds. We chose not to boondock.
The only reservations we had in Alaska were at Teklanika in Denali National Park. Other than that we played it by ear and made many decisions on the spur of the moment as to which way to go next. As others have said, take your time, drive slow, and be prepared to stop to take in the beauty all around you.
Our favorite place was Haines! Don't miss it! And don't be afraid to drive the Top of the World Highway!
You can see our
2013 Alaska trip campground list and posts about the trip on my blog.