Congrats on being 100% IU and planning a trip to Hawaii! As for TSA clearance, getting a TSA PreCheck number is a good idea if you want to make your airport experience smoother. I don't know about the Commissary Letter option, but you could also try applying for Global Entry, which includes TSA PreCheck and is a good fit for you. And if you're feeling fancy, you could always book business class flights for extra comfort on your journey. As for where to go to apply for TSA PreCheck or Global Entry, you can check out the TSA website for more info. Good luck, and have a great trip!