Purchasing your Alaska sportfish license prior to your trip has many advantages, and it's never been easier. By having this in your possession before arrival, you can avoid potential connectivity issues, printing hassles, and unnecessary delays.
To get started, visit the Alaska Department of Fish and Game Store. Once there you can choose to either log in, which is best for Alaska residents, or simply shop as a guest. Short-term non-resident fishing licenses are available for 1, 3, 7, or 14 days, with prices ranging from $15 to $75. You'll need a drivers license from your home state for identification, and you may need to purchase a King Salmon Stamp as well, so check with your guide before purchasing if possible.
Once payment information is processed and submitted, you'll have the option to digitally sign your license. If you have the means to do so, this is the best option as your license must be signed to be valid. Most laptops and desktop workstation computers have the capability to sign documents digitally via Adobe Acrobat or something similar. With a digitally signed license you can keep it on your phone, in the cloud, print it, and screenshot it, and all will be acceptable. If you can't sign digitally, you'll have to print a physical copy and sign it. After you do that, you can then take a picture of it and store it on your phone, in the cloud etc.
Some final considerations: Having your license on your phone or in the cloud is a great way to display proof should you be asked to do so. However, keep in mind that Alaska doesn't always have the same level of cell coverage you may be accustomed to - with multiple cruise ships in town simultaneously you may even have connectivity issues right in town. Cold conditions can also accelerate battery usage, so it's best not to put all your proverbial eggs in one basket. For the highest level of redundancy, I always print multiple signed copies of my license. I then place one in my waders, rain jacket, backpack, and any other pack, bag, or layer I may have on while fishing. These are stored in zip lock bags that don't take up any space at all.
If you still have questions, there's more information available online at the ADF&G web site. Do yourself a favor and have your license signed and printed before arriving in Alaska. You'll be glad you did!