I'm one who would say it's too late to leave. We have had full on snow-never-leaves serious winter in the first week of Sept. It's not normal but at the very least I would suggest you consider how you're going to bail out if it doesn't work. If winter hits you won't be concerned with a day or two of snow. You could find yourself in serious, continuous winter conditions. We do a race in late June that goes from Haines Jct to Haines and two summers ago the leg at the top of the pass was almost called for snow. I would hope that you would be able to hitchhike over some mountain passes and such but one of the things you might consider is a box with extra winter clothing in the event you need some gear beyond what you brought. I would, for instance, bring insulated over booties at the very least. No...I would probably bring boots of some sort and use spd pedals that flip to provide a flat side when it's too cold for clipless. From Anchorage to Fairbanks (using either highway direction) takes you over some passes that could very easily have snow in Sept. By the time you get into Canada it's a very high likelihood that you will indeed hit snow. I'm not sure that you will find -any- groceries from Tok to Haines Jct. Actually, now that I think about it, the grocery store in Haines Jct. is no longer open at all. Tok to Whitehorse will be at least one stretch where you'll most likely need to be almost entirely self contained. I would expect gas station food and a restaurant or two to be open in Haines and the restaurant in Destruction Bay may still be open with gas station food for sale. Best of luck and I have to close with the comment that as an Alaskan with a fat tire bike that rides occasionally down to -30F, I would never even consider leaving Anchorage at that time of year simply because I would not want to take all the clothing and gear needed to ensure a safe, trouble free trip. But that's just me and adventures are all about facing potential adversity so again, best of luck and drop a big note to the forums with your results.