You're on a motorcycle. I doubt you'll have many $300 fill ups. Gas stations, hotels, motels, restaurants, tire shops and even camp grounds take cards. By all means carry a hundred in 20's for convenience - but you're hardly in any risk of being robbed. Wild salmon in Alaska aren't that delinquent.
I've never been to Alaska yet but I have a hard time believing that you won't see an ATM/Bank or a Visa sticker on a window for extended periods of time. Or can't get to one within a couple days.
Numbers mentioned a good point. Zip lock bags. They are your friends.
I try not to carry more than I'm willing to part with.