A water bottle holder (or camel back) so you can drink as you ride, an MSR bottle of fuel just in case, tire plugs, small bicycle pump, good rain gear, and extra gloves. Those are pretty key for long stints. You can carry tools too, but other than adjusting your shifter or replacing a fuse you'll probably be looking at your credit card to get you home if anything happens mechanically to the bike.
I also recommend ear plugs or some good quality ear buds that block ambient noise help a lot with the wind noise. It might not be that bad for a few hours of riding, but spend 8+ hours on the bike for multiple days and that wind noise starts to take its toll.
Plan your stops accordingly to maximize efficiency and to leave yourself room in the fuel tank in case you get worse than normal fuel economy on a stint. You'll also learn the sweet spot for yourself the more you ride. I can push 200 miles between stops on my bike, but I've found that if I stop every 120-150 miles my stops are faster and I'm less sore at the end of the day. I've also learned that 650 miles is about as far as I want to go in a day if I have multiple days of riding ahead of me. I can go further, but it wears on me that much more.
For comfort I love having a full fairing. My windscreen is just under my line of sight and keeps me in a relatively clean air bubble. It also helps a lot with keeping bugs from hitting me in the face.